Sunshine Books Programming for education on the Commodore 64 a

programming

for education

on the commodore 64

a handbook for primary education

john scriven and patrick hall

programming

for education

on the commodore 64

a handbook for primary education

john scriven and patrick hall

First published 1984 by:
Sunshine Books (an imprint of Scot Press Ltd.)

12-13 Little Newport Street,

London WC2R 3LD

Copyright © Patrick Hall and John Scriven, 1984

All rights reserved. No part o f this publication may be reproduced, stored
in a retrieval system, or transmitted in any form or by any means, elec

tronic, mechanical, photocopying, recording and/or otherwise, without
the prior written permission o f the Publishers.

British Library Cataloguing in Publication Data

Scriven, John

Programming for education on the Commodore 64.

1. Education, Elementary

2. Commodore 64 (Computer)
I. Title II. Hall, Patrick

372. V 67 LB 1028.43

-----

Data processing

ISBN 0 946408 27 0

Cover design by Grad Graphic Design Ltd.
Illustration by Stuart Hughes.
Typeset and printed in England by Commercial Colour Press, London E7.

u

CONTENTS

Page

Program Notes vii

Introduction ix

1 Starting with Maths 1

2 Small is Beautiful... 27

3 Words, Words, Words 49

4 Making Friends with your Keyboard 69

5 Story Time 81

6 Logically Speaking 93

7 The Real Thing

107

iii

Contents in detail

CHAPTER 1
Starting with Maths

Starting off — the computer as calculator — choices and loops — pro
grams and randomness — Table 1: a table test — improvements — Table 2:
introducing time — using graphics and sound — looking for patterns —
Table Patterns: changing the display — Bingo: a game setting for a tradi

tional idea — repetitive learning — moving graphics to add interest —

Factor: a program to teach factorisation.

CHAPTER 2
Small is Beautiful...

Short programs and efficiency — Missing: find the numbers — ordering
numbers — Series: maths as an introduction to strategy — simplicity in
program structure — Number: a program to find a hidden number — using
graphics to brighten up simple ideas — Firework: a program to test general
numerical skills — the problems involved in learning fractions — Fraction:
a program to help with numerators and denominators.

CHAPTER 3
Words, Words, Words

Handling words on a computer — sorting things — Alphasort: a program
to sort words into alphabetical order — numbers in strings — Simon: a
game to improve memory — diversity of subjects in primary schools —
problems in spelling — different approaches — context clues — Hangman:
a multi-purpose spelling program — research skills — Anagram: clues

from word order.

CHAPTER 4

Making Friends with your Keyboard

Tackling entry errors — menus — making programs foolproof — moving
the character set — BigL: writing large on the screen — Keyboard: learning
the keys — Masking: changing binary numbers.

v

Programming for Education on the Commodore 64

CHAPTER 5

Story Time

Creativity — artificial intelligence — words at random — Story: a program
to help with creative writing and adjective use — interactive use of
computers — Gosh: more stories.

CHAPTER 6

Logically Speaking

Logical reasoning — problem solving — Treasure: finding pirates’ gold —
coordinates — using sound and sprites — Sonar: find the submarine.

CHAPTER 7

The Real Thing

Unique role of computer in simulation — the appeal of computer graphics
— simulation versus immediate experience — the realm of simulations —
Lock: an excursion on the canal — Power: electricity generation — inter
active simulations — elementary statistics — Coin: probability of
throwing a head — Cascade: Pascal’s triangle.

vi

Program Notes

All Commodore computers use special characters to control various func
tions on the screen. For instance, pressing the [CLR/HOME] key and

[SHIFT] will clear the screen. If those keys are pressed after a double quote

mark, an inverse heart will appear in the listing.

Although this is often a quick way to control print colours, inverse char
acters and cursor control, there are usually less confusing ways of achiev
ing the same effect. To avoid confusion in the listings, we have used these
codes as infrequently as possible. The exception is the use of SHIFTed
CLR/HOME to clear the screen as mentioned above.

To make the listings clearer, where this character appears, it has been

substituted by [SHIFT/CLR/HOME].

Note: Please be careful when entering programs listed in this book. The
quality of printing from a computer printer means that some characters

can look very similar — commas, in particular, can look very like full
stops.

In the program listings, } appears as

Vll

Introduction

The aim of this book was not originally to teach you BASIC. We had hoped
to let it contain educational programs which we ourselves had found
useful, and merely write about their use, as we have with the other books in
this series. As we were collecting material, however, we began to realise
that many people who used this book might have had little experience of
computers. For those that are new to computers, we have spent more time
introducing the early programs.

We hope to lead you step by step through the initial stages to simple
programming skills. These are combined to produce short programs that
show how the Commodore 64 can be used at home or at school to make
learning more interesting, while also discovering something about the
computer itself.

The 64 is a very advanced microcomputer and has some outstanding
features. Unfortunately, these are not accessible from BASIC without
addressing the memory directly, and this makes some aspects of the 64
more obscure than they need to be.

We will attempt to show you that these drawbacks can be overcome, and
that you will be able to write interesting educational programs once you
have understood a little more about how the 64 operates. If something is
not clear straight away, come back to it at a later stage and with luck you
will understand it.

Above all, this is a book about doing. No one ever learned about
computing simply by reading a book, so do try out the examples and alter
things as you find necessary.

If you have some experience with computers, you can skip some of the
introductory material and dive into the meatier sections. We hope that you
won’t be content simply to copy out the listings, but will modify and adapt

the programs and routines to suit your own needs.

All the programs have been tried and tested, and are printed from the
actual listings, so they should work first time. If they don’t, it’s probably

due to a tiny typing error that’s escaped your notice. Check the listing

against the book, as even a missing semicolon can stop the program. If, in
spite of this, you still find something doesn’t work as expected, we’d like to
know about it!

Ultimately, we hope that you will continue to enjoy your computing and

that this book will help you achieve your aims.

IX

CHAPTER 1

Starting with Maths

Starting off — the computer as calculator — choices and loops —

programs and randomness — Table 1: a table test — improvements

— Table 2: introducing time — using graphics and sound — looking

for patterns — Table Patterns: changing the display — Bingo: a game

setting for a traditional idea — repetitive learning — moving
graphics to add interest — Factor: a program to teach factorisation.

Ten years ago, it was unusual to find calculators in schools, let alone
computers. The advent of the home computer, and computers in schools,
brings with it the responsibility to make sure a) that the users are familiar
with them and b) that they are used wisely.

In this chapter we shall be looking at how computers use information,
and how they can display this. If you have some knowledge of computers,
then you can skip over the early sections. If you are coming to the 64 as
your first machine, then it should clear up some of the mysteries of how
computers can make simple decisions and appear to act intelligently.

If you have used a calculator, then you know that you enter data, in the

form of numbers, along with operators, like plus or minus, to tell the calcu

lator what to do with those numbers. For instance,

2+ 2 - 1=

At each stage of the calculation, the display shows the last number entered

or the result at that stage. You can use the 64 as a calculator in the same
way. Instead of calculator buttons, you can communicate with the 64 via
the keyboard. If you enter

2 + 2 -1 [RETURN]

it will calculate the result. (The [RETURN] key can be seen as sending the
information you have entered inside the computer.) The problem is that,
whereas you see the result automatically on a calculator, the 64 has to be
told to display the answer. To speak to the computer, you have to use the
language that it understands. The 64 uses the language BASIC, which is a

1

Programming for Education on the Commodore 64

fairly small set of words that are quite close to normal English. These
words are entered via the keyboard, just as on a normal typewriter.

To make the 64 print something, you must use the PRINT statement. If

you enter

PRINT 2 + 2 -1 [RETURN]

then the result, 3, will appear on the screen.

PRINT can be used to write words on the screen in just the same way. If

you enter

PRINT “ YOGI BEAR” [RETURN]

then the words YOGI BEAR will appear on the screen.

This is using the computer in immediate mode, which is handy for
instant calculations, but is hardly using it in the manner for which it was
intended.

The most useful point about computers is that they can store the instruc
tions given to them and follow them in the correct order.

So that they can follow the instructions in the correct order, the instruc
tions are given line numbers. First make sure there’s nothing already in the
64’s memory by typing NEW [RETURN]. To perform the simple example
earlier, you could use the following:

10 PRINT “ TWO PLUS TWO TAKE ONE EQUALS” ; [RETURN]

20 PRINT2 +2 - 1 [RETURN]

If you enter the lines as they are written, the program lines are stored in the
computer’s memory.

{Important: Make sure that you enter the lines exactly as they are written.
Humans can understand things even when there are mistakes, but
computers are unforgiving and even putting a letter 1 instead of a figure 1,
or a letter O instead of a figure 0, will prevent program instructions from
working.)

To execute the instructions, the command RUN must be entered and the

[RETURN] key pressed. The computer will obey the instructions in each
line in turn, that is, print the sentence in quotes in line 10 followed by the
answer to the calculation in line 20. As there are no more lines, the program
will end there, and pass control back to you. (From now on remember to
press the [RETURN] key at the end of program lines and after commands.
There won’t be any more reminders!)

Programs, then, are simply lists of instructions that the computer obeys
in a particular order. It doesn’t matter in which order you enter the lines,
the computer sorts them out for you. So if you now enter

2

Chapter 1 Starting with Maths

5 PRINT “THIS IS MY PROGRAM”

it will be executed first. RUN the program to test this.

If you use the command LIST, the program you have been entering will
appear on the screen in the correct order. To get rid of one particular line,
enter just the line number. So, entering

5 [RETURN]

followed by LIST, will show you that line 5 has indeed been deleted.

To delete a whole program from memory, use the command NEW. This

clears the complete BASIC program, so don’t use it unless you’re sure

that’s what you really want.

Try it now and check that your program really has disappeared by LIST-

ing it.

Inputs and variables

As well as entering information in program lines, you can enter it via the
keyboard during the course of a program. The 64 stores this information in
the form of variables. This is just a way of saying that letters can stand for
various values, like in algebra. If you say X + 6 = 10, then X must have the
value 4. In the language BASIC, you can assign a value to a letter by simply
saying X = 4.

Enter the following

X = 4

Now, as a direct statement, enter

PRINT X

The value 4 will be printed on the screen.

X is known as a variable. If the variable is going to stand for something

in particular, then it’s a good idea to use a longer name, for instance, the
variable to hold a year could be YEAR = 1984.

The 64 will only recognise the first two letters of the variable, so YEAR

and YELLOW appear the same to the computer. If you enter

YEAR =1984

then

YELLOW = 6

Programming for Education on the Commodore 64

then

PRINT YEAR

the result 6 will appear, so be careful how you use variable names.

If you want to store a string of characters, ie letters, numbers, graphic
characters, or anything else on the keyboard, you have to use what is called

a string variable. This is just like a numeric variable except that it ends in a

$.

Enter this:

A$ = “ CBM 64”

PRINT A$

The string variable A$ now contains the string of characters CBM 64, so
when you tell it to print out A$, that is what is printed.

Just as it is a good idea to use meaningful names for numeric variables,
string variables too are easier to understand when they mean something.
For example, NAMES is more meaningful than N$.

Remember that the 64 will confuse NAMES with NAILS, as it only recog
nises the first two characters. It is also important that the variable name
should not contain a BASIC keyword. This means that FORT is not
allowed — it contains the BASIC word FOR. The variable BRIGHTONS is
not allowed as it contains the word TO.

As was mentioned earlier, variables are useful when you want to enter

information during the course of a program.

10 PRINT “ ENTER YOUR NAME”

20 INPUT NAMES

30 PRINT “ HELLO, ” NAME$

40 PRINT “ENTER YOUR AGE”

50 INPUT AGE

60 PRINT “ MY! YOU DON’T LOOK ” AGE;NAME$

This program, when RUN, will tell you to enter your name at line 10. In line
20, it will stop program execution until it receives an input, followed by a
press on the [RETURN] key. Whatever is entered in this line becomes

known as NAMES, and will be printed out in line 30, after the word
HELLO.

Line 40 will print the request for the age on the screen, and this will be
stored as variable AGE in line 50. Note that you must enter this in figures or
the computer will tell you to REDO the input. Line 60 will print out the text

in that line plus the name and age that were entered. The semicolon

between AGE and NAMES is important to separate them.

4

Chapter 1 Starting with Maths

To save entering RUN again and again, it is possible to send program

control back to the beginning. To do this, add the program line

70 GOTO 10

This will cause the program to go into a never-ending loop. To get out of
this, it is necessary to press the RESTORE key while holding down the
RUN/STOP key at the same time.

If it’s at all possible, avoid using GOTOs in your programs. Although in

Commodore BASIC you have to use them sometimes, they can make the
structure difficult to understand.

Some programs

Now that you can use variables and inputs, you can start to use your 64 to
write simple programs, and also make them appear more friendly. Note
that, in line 10, the INPUT statement can include words that are printed.

10 INPUT “ WHAT IS YOUR NAME” ;NAME$
20 INPUT “ WHAT IS THIS YEAR IN FIGURES’’;YEAR
30 INPUT “ WHAT IS THE YEAR OF YOUR BIRTH’’;BIRTHYEAR
40 INPUT “ HOW OLD ARE YOU” ;AGE
50 IF AGE = YEAR-BIRTHYEAR THEN PRINT “ I’LL BELIEVE

YOU’’:STOP

60 IF AGE = YEAR - BIRTHYEAR - 1 THEN PRINT “ I’LL

BELIEVE YOU’’:STOP

70 PRINT “ I DON’T BELIEVE YOU’’

The semicolons in INPUT statements are essential to avoid a SYNTAX
ERROR message. Notice too that you don’t need to put a question mark
in; this is automatic when the 64 expects an input. You should understand

this program down as far as lines 50 and 60. In these lines, the computer
checks to see if the entered age, AGE, is possible. Line 50 is for those who
have already had their birthdays this year, and line 60 is for those whose

birthdays are yet to come. IF the line is true, then a message is printed out,
and the program stops.

Note the use of a colon to separate two statements on the same line. If

neither line 50 nor line 60 is true, the program continues to line 70, where

the final message is printed out, and the program stops as there are no more
lines left to execute.

The IF .. .THEN statement is the first statement that you have come

across that gives your 64 some intelligence. At last it can make decisions

according to different circumstances. You can imagine almost any human

activity being governed by I F .. .THEN rules.

5

Programming for Education on the Commodore 64

IF the alarm goes THEN get up.

IF it’s raining THEN go back to bed.

These statements are very useful in a program, as they can test for correct

answers to problems posed by the computer.

10 Question

20 Answer

30 IF Answer = right THEN PRINT “ OK”
40 IF Answer = wrong THEN PRINT “SORRY”

50 Next Question

60 Next Answer
70 IF Answer = .. .
etc.

Loops

In the last program, if you had wanted ten questions, you would have had
to repeat the same structure as in the first four lines ten times. As well as
being wasteful on memory, this would take a long time to enter. Luckily,
you can employ a loop to take you through the same section of program a
certain number of times. The only loop that the 64 possesses is the FOR...
TO ...NEX T loop. Although it looks complicated, it’s really quite a
simple idea.

You need to set up a counter in one program line at the beginning of the
loop, and to have a marker line to show the end of the loop. This example
should explain it more clearly. First type NEW to get rid of the last
program.

10 PRINT “ LOOP STARTS NOW”
20 FOR N = 1 TO 10
30 PRINT “ LOOP NUMBER ”N

40 NEXT N

50 PRINT “ LOOP FINISHED NOW”

When the program is RUN, line 10 simply prints a message. Line 20 means
‘Set a counter up called N. Start counting from 1 until you reach 10.’ Line
30 prints out the number of the loop, which is 1. Line 40 means ‘Increase N

by one and go back to the start of the loop. ’ N is therefore now 2. Program
control goes back to the start of the loop in line 20; line 30 prints out LOOP

NUMBER 2, N is increased once again, and so on. At the end of the tenth

time through the loop, N becomes 11. When the program returns to line 20,
the program says ‘The loop is only supposed to go up to 10, so program

6

Chapter 1 Starting with Maths

control must jump straight to the first line after the end of the loop’, ie line

50, and the final message is printed out.

If you enter this short program, and RUN it, you can see this in opera

tion. After it has stopped, enter PRINT N, and you will see that it does

indeed contain the value 11.

When a program is RUN, all the numeric variables are set to zero, and

the string variables emptied, so you can run the program again and again.

Random numbers

If you want the computer to ask specific maths questions, you now have all
the knowledge you need. It’s far more useful to have it select the questions
out of a hat, however, and there is a very useful facility to let it do just that.

If you enter PRINT RND(O), then a number between zero and one will
be printed. This number is chosen at random, and the value can be assigned
to a variable.

10 FOR N = 1 TO 10
20 X = RND(O)
30 PRINT X
40 NEXT N

This program will print out ten random numbers between zero and ten.
Numbers this small may not be much use in simple number problems, so
line 20 could be changed to

20 X = RND(0)*100

Note: Computers use an asterisk (*) for multiply so that this won’t be

confused with the letter X. The divide sign is an oblique line (/).

Line 20 will now generate numbers between zero and 100. If you RUN
this now, you will see that the numbers are so random that they have several
decimal places. To lose the decimal part of the number, change line 20 to

20 X = INT(RND(0)* 100)

This will generate integers, or whole numbers between zero and ninety-

nine.

At this stage you know how to generate numbers at random, how to loop

ten times to produce ten questions, how to input answers and how to check

that the answers are correct. You can combine all these points in a program
designed to test knowledge of one aspect of maths.

7

Programming fo r Education on the Commodore 64

Table 1

10 RE M
20 R E M * * * TA B L E T E S T ** *
30 R EM

100 SC = 0

110 P RINT" [S HI FT / CL R/H OM E1 "

120 P R I N T T AB< 1 2 ) " TA B L E TEST "

130 F O R N = 1 T O 10

140 A = INT(RN D (0)* 13)

150 B = I NT(R N D (0)*13)

160 P R I N T TAB< 4-N*.1 1 ); N; " ■) "A" X "B T A B (2 4

170 I NPU T G

180 IF G = A * B T H E N PR I N T TA B(3 0 ) "OK"

190 IF G = A* B T H E N S C =S C
20 0 IF G < > A * B TH E N P R I N T T AB( 3 0 ) "NO - " 3 A* B
21 0 N E XT N
220 P R I N T "Y O U SCO R E D ";SC
23 0 P R I N T" P RE S S SP A C E BA R TO GO"
240 GE T Z$
250 IF 7.$="" T H E N G O T O 240
26 0 G O T O 100

READY .

+ 1

) " = " 5

Commentary

Line 100 sets the variable SC, which holds the score, to zero.

Line 120 uses the TAB statement. This moves the print position across the
screen.

Lines 140 and 150 choose two numbers between 0 and 12 at random.

Line 160 prints the question on the screen. Lines 170 to 200 accept an input
and check it against the correct answer.

Line 190 increments the score by one. Lines 220 to 260 print the score and
allow the user to go again.

In the past, computers have always been associated with mathematics and,
even nowadays, computers tend to be used more in the maths and science
departments of schools. In fact, computers are good at operating with any
kind of symbols, not just numbers, and it would be a pity if their ‘number-

8

Chapter 1 Starting with Maths

crunching’ capability were the only thing they were used for in the edu
cational sphere.

In spite of this, maths is an area where a simple introduction can be
made. This is also an area where it is easy to write programs that test recall
without being truly educational. It has been shown by many educational
psychologists since the war, such as Jean Piaget and Jerome Bruner, that
children develop by passing through distinct learning stages. They cannot
learn automatically, but need much practical experience before being able
to manipulate symbols in their minds and finally achieve a stage of logical,
formal thought. The computer in its present form cannot replace practical
experience, but its graphic capabilities can help tremendously where the
child begins to learn to use symbols or concrete images rather than the
objects themselves.

We have tried to avoid as far as possible the type of program that uses a
computer to do what can be just as easily achieved using traditional mater
ials. Computers are expensive artefacts to have around without careful
thought being given to their most profitable use, whether at home or at
school.

You may think that we have spent some time on showing you how to
write a program that we are now tearing to pieces. The traditional table test
is, unfortunately, an example of a weak, drill-type program. The reason it
is included here is that it demonstrates simple principles of program design
and is easy to understand.

If this was the only sort of program you were ever going to write, we
would consider that we had failed in our aim to introduce a more dynamic
approach to using computers in education. It is true that it merely tests
recall, without reinforcing correct answers, diagnosing problems or
attempting to offer help. It can, however, be used with caution, provided
these shortcomings are realised.

Instead of leaving you with the simple version of the program, here is a
listing that attempts to go one step further. It produces the numbers at
random, but starts a time at the first question, so the user has a target to
aim at, in trying to better his or her previous time. Also included is a facility
for the teacher or parent to check the results of each program run and to
compare the times taken.

Table 2

10 REM ** ,7. SC RIVEN **
20 REM
30 REM ** 10/10/82 **
40 REM
50 REM ** TIMED TABLE TEST **
60 REM
70 REM ** IN ITIALIZATION **

Programming for Education on the Commodore 64

80 REM
85 REM
90 DIM NA$(30 )

100 DIM S C (30)
110 DI M T M (30)
120 NU = 1
130 FL = 0
140 REM
150 R EM ** TES T LO OP **
160 RE M
170 FO R NU = 1 TO 30
180 P R I N T" C S H I F T /C L R / H G ME3 "
190 PR IN T T A B (12) "T ABL E TEST"

200 P RI NT T A B ( 10 )" ENTER YOUR NAME "

210 INP UT NA *(NU)

220 P RI NT "OK, "; NA$(NU )

230 PRINT "PRE SS S P AC E B AR TO BE GIN "

240 G ET Z*

250 IFZ$="" THE N 2 40
260 SC (NIJ) =0
270 TS=TI
280 P R I N T " C S H I F T /C L R /HOM E 3"
290 P RI NT T A B (12 )" TAB LE TEST"
300 PRINT T AB( 1) NA *( NU )
310 FOR N = 1 TO 10
320 A = I N T (R N D (0)*13)
330 B « TNT (RN D (0) * 13)
340 P RI NT T A B (4— N * . 11 );N 5 "-)“A " X "B T A B (
350 INP UT G
360 IF G = A* B TH E N PRI NT T A B (30 )"OK"
370 IF G = A*B TH EN S C( N U ) =SC ( N U ) +1
380 IF G <> A* B T HE N PRINT T A B (30)"NO- ";
390 N EX T N
400 T T = I N T ( (TI-TS)/60)
410 P R I N T N A t (NU ) ;" SCOR ED " ;SC(NU );
420 PRINT" OUT OF 10 IN ";T T ;" SECS"
430 TM (N U) = TT

440 P R IN T "P R ES S SP AC E BAR FO R A N OT HE R GO"
450 G ET Z$
460 IF Z'$="" TH EN GO TO 4 50
470 IF Z$=".V‘ T HEN GO TO 1000
480 N EXT NU
490 P RIN T"C LAS S COMPLE TE D"
500 FOR M = 1 TO 2000s NEXT M

1000 REM
1010 R EM ** RE SUL TS R OU TI NE **
1020 R EM
1030 PR IN T "C S HI F T/ C LR / HO M E3 "
1040 P RI NT T A B (15 )"R ESU LTS"

24) "

A*B

10

Chapter 1 Starting with Maths

1050 PRINT
1055 PRINT
1060 PRINT T A B (5)"NAME ";TA B (24)"SCORE ";T A B (34)

1070 PRINT
1080 FOR NU = 1 TO 30
1090 PRI NT NU5 T A B (5)N A $ (N U )5 TA B <24)SC( N U);T A B (34)

1100 IF NU = 15 THEN PRINT"PR ESS SP ACE BAR TO

1110 IF NU = 15 THEN GET Z$

1120 IF Z$ = "" THEN 1110

1130 NEXT NU

READY.

"TI ME”

TM(NU)

CONTINUE"

Commentary

One exercise, often given to children learning tables, is to discover the
patterns that the answers make when these numbers are shaded in on a grid
of figures. It is usual to make the grid 10 x 10 or 12 x 12, and this idea forms
the basis of the next program.

There are many ways in which the 64 could be told to draw a grid of
numbers on the screen, such as printing each line separately. A neater way,
that uses more of the computer’s in-built functions, would be to put the
print routine in a loop. If you simply entered

FOR N = 1 TO 200:PRINT NrNEXT N

the numbers would certainly appear, but they would not be formatted in
neat lines with units and tens underneath each other. If you consider the
screen layout on the 64, you will see that the numbers could fit in very
regularly. The screen is 40 characters in width, and the largest number
takes three figures (2,0 and 0). If a space is left between each column, you
can see that ten numbers, each one preceded by a space, will exactly fit on
each line.

HTU HTU HTU HTU HTU HTU etc.

If we could tell the 64 to PRINT AT a particular row and column posi
tion, it would be easy. Unfortunately, such a command does not exist in
Commodore BASIC. Luckily for us, however, there is such a routine
buried inside the operating system. Near the top of the memory lies the
kernal. This is a table of routines that jump to different parts of the
memory to perform particular functions. The one we are interested in is
called PLOT and lies at location 65520. All you need do is load two regis

11

Programming for Education on the Commodore 64

ters with the row and column values by POKEing, and then call the kernal
routine PLOT. You can do this in one line:

POKE 782,X:POKE 781,Y:SYS 65520:RETURN

and GOSUB this routine just before you print something. The new print

position will be at the X and Y coordinates you have just entered. This is a
very useful routine and you will find it occurring quite frequently in these

programs. In the next program, it is used to move the print position across

to each new column and row.

When the numbers have been printed, the user is asked to enter the table
that is required. So that these numbers show up, the next routine changes

the colour of just these numbers to white. Again, this is not a very complex
task. The 64 stores the screen text in one set of locations, and the colour in

which the text appears in another. The second set of locations starts at

55296. As the grid of numbers is spaced evenly, starting at every fourth

location, the colour value can be POKEd in another FOR... NEXT loop.

How can you tell it to act only on the numbers in the particular table

chosen? A useful trick is to test if there is a remainder after division by the
table number. If this seems difficult to grasp, try this program:

10 INPUT A
20 FOR N = 1 TO 100
30 IF INT(N/A) = N/A THEN PRINT A

40 NEXT N

This runs through the numbers from 1 to 100, and divides each one by the
number you input. If the number has a remainder, the INT function will
round down to the nearest whole number below, eg INT(11.5) = 11. It will
only print those numbers that don’t have a remainder, as the INTeger of 12

is 12.

Notice that this program tests the codes of keys that are pressed in GET

statements. If any key other than the numbers 1 to 9 is pressed, the program

loops back to ask for the key to be pressed again.

Table Patterns

10

REM

*#*

TABLE

PATTERNS

***

20 REM

30 REM

***

A.J.S.

, 4/10/83

*•#*

40 REM
50 REM

60 REM

12

CLEAR SC RE EN +

Till.

Chapter 1 Starting with Maths

70 REM
8@ PR I NT " C SHI FT / CL.R / HOME 1 "
90 X =0:Y=0 5G OSU B540

100 P R I N T"TABLE P A T T E RNS"

110 X=2: Y~2

120 REM
130 REM *** LOOP TO PRINT NUMBERS ***

140 REM

150 FOR N * 1 TO 200

160 IF N=10 OR N=100 THEN X = X-1

170 60SUB 5 40:F’RINTN
180 X ~ X + 4'

190 IF I N T(N /10 )= N /10 THEN X-l
200 IF I NT (N / 10) -~N / 10 THEN Y=Y+1

210 IF I N T (N /10)= N /10 AND N>99 THEN X=0
220 NEXT N

230 REM

240 REM *** SELECT TABLE ROUTIN E ***
250 REM

260 POKE 198,0

270 X = 5:Y « 23 :GO SUB540

280 P R INT"*PRESS THE TABLE NUMBER*"
290 GET AT:IF AT = "" THEN 290
300 A-~VAL.. (AT)

310 IFAC 1 THEN 260

320 X= 30: Y=0 :GOSUB540:PR I N T "T A BLE"A "
330 REM

340 REM *** CHANGE NUMBER COLOUR S ***

350 REM

360 COL = 55296
370 FOR N = 1 TO 200

380 IF INT(N/A) <> N/A THEN 420
390 POKE COL.+81 + (N- 1) *4,1

394 REM

400 POKE COL+ 81+(N--1)*4+1,1

410 POKE CO L +81+ < N -1)*4+2,1

420 NEXT N

430 X=5:Y = 23:GOSU B540

440 POKE 198,0

450 PRIN T"PRESS SPACE BAR TO CLEAR"

460 GET AT:IF AT = "" THEN 460

470 FOR N = 55296 TO 56319

480 POKE N ,14

490 NEXT N

13

Programming for Education on the Commodore 64

500 GOTO 260

510 REM

520 REM *** "PRINT AT" SUBROUTI NE ***

530 REM

540 P0 K E 7 82 ,X s P 0 KE78 1,Y s SYS6552 0s RETURN

RE A D Y.

Commentary

Line 80 clears the screen. Line 90 sets the X and Y coordinates to zero.

Lines 150 to 220 contain the loop that prints the table grid.

Lines 190 to 210 move the print position at the end of the line — when the

value of N is exactly divisible by 10.

Lines 260 to 310 allow the number of the table to be input. Line 320 prints

the table number at the top of the screen.

Variable COL is the location of colour memory. Lines 370 to 420 change

the text colour by POKEing the relevant memory locations. Line 380 skips

over the POKEs if the value of N is not exactly divisible by the table chosen.

Line 540 contains the ‘PRINT AT’ subroutine.

Lines 280 and 450 contain the same number of characters in the print

statements so that they can print on top of one another.

Bingo

After the element programs in this chapter, we move on to a couple in the

area of maths that extend the use of the 64’s features. If you are fairly new

to BASIC, you may find the ideas more difficult to grasp. Although they
are explained in some detail in the program notes, you may prefer simply to
type in the listings. As your skills improve in the following chapters, you
can come back to these programs at a later stage.

Bingo is an attempt to move beyond the simple approach of answering
questions on screen. The child is presented with a game format, and,
although the questions still only test recall of previously-learned know

14

Chapter 1 Starting with Maths

ledge, there is a reward motive in completing the whole card. When this
stage is reached, there is a visual display.

There is always some problem over how many of a computer’s facilities
need to be incorporated in every program. Just because Commodore
computers support voice synthesis, high-resolution graphics and music in
three-part harmony, it does not mean that a good program has to possess
all of these features, or indeed any of them. A happy medium has to be
reached at the planning stage. Some programs benefit from using specialist
features, but usually take more time to program. In some cases, their
implementation can be irritating and work contrary to the expectation of
the teacher or parent.

One example is the addition of loud sound effects, which can be disturb
ing in a classroom if there are other children engaged in quiet activities. If
this is the case, removal of the offending sound commands will prove an
answer. An alternative, of course, is to reduce the volume by use of the TV
volume control! Flashing displays should usually be avoided. Where
sections of the screen are required to flash, this is done to draw attention to
part of the display. Having had personal experience of a child suffering a

petit mat attack due to the program loading display on a cheaper computer,

we are particularly aware of this possibility. Also, overuse of this feature
is likely to prove distracting in many cases.

10 REM BIMBO - PAT HALL, JAN '84

20 REM
30 GO SUB 110 * REM INITIA LI SA TION

40 GOBUB 330 : REM SET UP
50 GOSUB 770 : REM TEST-
60 GOSUB 1150 s REM REWA RD
70 GOTO 40
80 END
90 REM INITIALISATION

100 REM SET UP ARRAYS
110 DIM A( 20 ) : DIM B < 20 )
120 DIM C( 20 ) s DIM D( 20 )
130 DIM L B ( 20 )
140 REM SELECT LOCATIONS FOR BOXES
150 N = 0

160 FOR I = 1144 TO 1180 STEP 9
170 FOR J = 0 TO 600 STEP 200
180 N N + 1

190 L B ( N ) = I + J
200 NEXT J
210 NEXT I

15

Programming for Education on the Commodore 64

220 REM INITIALISE GAME AMD SCORE
230 6 » 0 s S * 0
240 REM WHITE SCREEN
250 POKE 53280, 1 s POKE 53281, 1
260 PRINT ""
270 REM SWITCH ON EXTE NDED COLOUR MODE
280 POKE 53265, 91
290 RETURN

300 REM

310 REM SET UP GAME

320 REM YELLOW BAC KGROUND
330 POKE 53282, 7
340 REM PUT TITLE ETC.. ON SCREEN
350 PRINT CHR'-T ( 144 )
360 X » 14 s Y - 0 : GOSUB 710
370 PRINT "<< BINGO >>"
380 PRINT CHRT < 28 )
390 X - 0 : Y = 1 : GOSUB 710
400 G = G + 1

410 PRINT "GAME "$ G

42.0 X = 31 : GOSUB 710
430 PRINT "SCORE ” r, S

440 FOR I = 1 TO 20
450 REM INITIALISE FLAG
460 D< I ) = 0
470 REM CALC UL ATE NUMBER

480 A ( I ) = I N T ( R N D ( 1 > * 8 > + 2

490 B ( I ) = I N T < R N D ( 1 ) * 5 ) + 5
500 C< I ) = A ( I ) * B < I )

510 REM PLACE BOX ON SCREEN

520 FOR J = 0 TO 3

530 FOR i< = 0 TO 80 STEP 40

540 L = LB ( I ) + J •+• K

550 POKE L + 54272, 7 ; POKE L, 96

560 NEXT K

570 NEXT J
580 REM PLACE NUMBER IN BOX

590 REM RED FOREGROUND
600 POKE L B ( I } + 54313, 2
610 POKE L B ( I ) + 54314, 2
620 E = I N T ( C< I > / 10 ) + 112
630 POKE L B ( I ) + 41, E
640 E = E - 112
650 E = C( I ) - E * 10 + 112

16

Chapter 1 Starting with Maths

660 POKE LB < I ) +42, E
670 NEXT I
680 RET URN
690 REM
700 REM PRINT TAB ROUTI NE
710 POKE 782, X. s POKE 781, Y
720 SYS 65520
730 RETURN
740 REM
750 REM TEST ROUTINE
760 REM CHOOSE ONE BOX AT RANDOM

770 T = INT( R N D ( 1 ) * 20 ) + 1

780 REM CHECK BOX IS STILL ON SCREEN
790 IF D( T ) = 1 THEN 770
800 DI T > = 1
810 X = 9 s Y = 22 s GOSUB 710
820 PRINT "WHAT IS" AIT) "X" BIT)

830 X. = 30 : GOSUB 710
840 PRINT "
850 X = 30 : GO SU B 710
860 INPUT AN* s AN = VAL I AN* )
870 IF AN <> Cl T ) THEN 830
880 REM INCREASE SCORE
890 S = S + 1
900 X -■ 37 : Y = 1 : GOSUB 710
910 PRINT S
920 REM SOUND EFFECT, VOICE 1
930 POKE 54296, 15 : REM VOLUME
940 POKE 54277, 136 : REM ATT / DEC
950 POKE 54278, 136 ; REM SUST / REL

960 POKE. 54276, 17 : REM W AVEFORM
970 POKE 54273, 76 : REM HIGH NOTE
980 POKE 54272, 252 : REM LOW NOTE
990 FOR I = 1 TO 100 s NEXT I

1000 POKE 54277, 0
1010 POKE 54278, 0
1020 POKE 54276, 0
1030 REM ERASE BOX
1040 FOR I = 0 TO 3
1050 FOR J = 0 TO 80 STEP 40
1060 L = LB I T ) + I + J
1070 POKE L. + 54272, 1 : POKE L, 32
1080 NEXT J
1090 NEXT I

17

Programming/or Education on the Commodore 64

1100

1110 FOR I

1120

IF I N T<8/20) < > S / 20

= 1

RETURN
1130 REM
1140
1150

REM REWARD ROUTINE

PRINT

it l l

1160 RESTORE
1170

FOR I
1180 READ

1190

FOR J == 0 TO 1
1200 FOR K
1210

1220
1230
1240
1250

1260
1270

1280

POKE
POKE
NEXT K
NEXT
NEXT I
FOR I = 1 TO 3000
PRINT
RETURN

= 1

N

= 0

N + J
N + J

J

H M

1290 REM
1300

1310 DATA

REM D

ATA FOR 'BINGO'

1024, 1104, 1184,
1320 DATA 1424,
1330 DATA 1824,
1340

1350

1360

1370

1380
1390
1400
1410
1420
1430 DATA
1440
1450
1460 DATA
1470
1480

1490

1500

1 51 0

1520
1530

DATA 1190,
DATA 1548,
DATA 1868,
DATA
DATA

1274, 1354, 1434,

1674, 1754, 1834, 1914, 1038

DATA 1118 ,
DATA

1518, 1598,

DATA 1918, 1080,
DATA

1401 ,

1801 ,

DATA

1284 , 1364,

DATA 1684,

1209, 1289,

DATA 1609,
DATA 1 1 3 3,
DATA 1773, 1853,
DATA 1298,
DATA 1698,

1

DATA
DATA

.1. a

1622, 1702,

THEN 770

TO 1000

: NEXT I

TO 115

TO 40 STEP 40

+ K +
+ K, 1

54272,
28

xi

s NEXT I

1264,
1504 , 1584, 1664, 1744
1904,

1026,

1068, 1110
1270, 1350, 1388, 1466
1590, 1670, 1750, 1830
1906, 1034, 1114,

1514,

1198,

1278,
1678,
1161 ,

1481 , 1561 ,

1358, 1438

1758,

1241 , 1321

1641 ,
1882, 1044, 1124, 1204

1524,
1764,

1444,
1844, 192.4,

1369, 1449, 1529
1689, 1769, 1849,
1213,

1612,

1614,

1931 , 1138, 1218
1378,

1458, 1538, 1618
1778, 1858, 1060, 1142
1302, 1382, 1462,

1782, 1862, 1940

1344

1194
1594

1838

1721

1604
1129

1051
1693

1542

18

Chapter 1 Starting with Maths

Commentary

The program is controlled by lines 30-80. Line 70 causes the program to
continue indefinitely until RUN/STOP is depressed.

Lines 100-290 form the first subroutine of the program, called by line 30
in the control module. The routine initialises various variables needed by
Bingo. Five arrays are set up. The A and B arrays hold the twenty pairs of
numbers presented to the child and the C array stores the answer for each
multiplication. The D array consists of flags, one for each number pair,
which ensure that the same question is not repeated. Finally the LB array
stores the screen locations of each coloured box the numbers are printed in.
The actual value of each member of the LB array is the location of the top
lefthand corner of the coloured box. These values are calculated by the
two nested FO R .. .NEXT loops between lines 160-210. Here the values
that the I and J loop variables STEP through are arranged so that their
sum, I + J, gives the exact location. Note the way in which the variable N is
incremented through the loops to identify each box.

This first subroutine also sets the values of S (the score achieved by the
child) and G (the number of ‘sheets’ completed) to zero. Line 250 sets the
entire screen area to white and then line 280 switches on the Commodore
64’s ‘extended’ colour mode. This allows text to be printed with a different
background colour to the screen background (and is the equivalent of the
command COLOUR (colour +128) in BBC BASIC). Extended colour
mode is switched on with POKE 53265,91 and off with POKE 53265,27. It
allows three more background colours to be set up simultaneously on the
screen, but requires a different character set for each.

Lines 310-680 present the bingo sheet. Use is made of the PRINT TAB
routine at lines 700-730. This allows an easy way to format the display. X
and Y screen coordinates have to be defined before calling the routine and
this is done here, for example, at line 360. Lines 480-500 calculate the
questions and answers and the boxes are drawn by lines 520-570. The J
and K values in the two nested loops increment the value of LB calculated
before, and this value is then POKEd to screen and colour map by line 550.
Each number is placed in its box by 600-660. Extended colour mode is
used and the two-digit numbers have to be separated by the simple arithme
tical routine into the individual ten and unit figures. These are POKEd
separately to the screen.

Lines 750-1120 present the test. The Tth box is chosen at line 770 and the
flag is checked by line 790 to make sure that box and question have not
already been chosen. The TAB routine is used again in presenting the ques
tion and the child’s input is error-trapped. A sound effect is produced and

19

Programming for Education on the Commodore 64

finally the box itself is erased by lines 1040-1090. Line 1100 tests when the
entire screen is cleared.

The reward routine simply places the word ‘Bingo’ large upon the screen.
This is done in a very similar way to the drawing of the boxes but here the
location of each ‘box’ is not calculated but held as lines of DATA which are
READ by line 1180. The nested loops between 1190-1240 draw each
section of the letters.

Factor

The last program in this chapter, Factor, extends the approach to that of a
video game. It does not require high-speed manual dexterity, however,
simply the ability to input any factor of a number that appears on the
screen. The number is successively factorised by the inputs until it reaches

1, when another number is chosen. If the factor chosen is permissible, a
plane flies across the screen and drops a bomb on to the number resulting in
an explosion. If the number is incorrect, the bomb misses. There is also an
on-screen scoring facility.

A last point needs to be made about the type of reward offered in a
program. Although an exciting display may offer positive reinforcement
to the child, it is hoped that the reward will become intrinsic, ie that the
child enjoys the success of getting a problem right without any external

reward. When adults succeed in solving a ‘whodunnit’, or complete the
Times crossword, the achievement alone is enough. This internalisation
has taken a long time to achieve, however, and praise, even from a

machine, is important!

It is also necessary to point out incorrect responses in a gentle manner, or

the child feels despondent and even aggressive. If a computer has ever

beaten you at chess, you will know the feeling. Although it may seem

obvious to state, the difficulty of the problem has to be within the solving
capacity of the child. When designing programs, the incorrect response

should not result in a screen display that is more impressive than that for a

correct response, or the reinforcement effect will be lost, as the child

attempts to fail because the display is prettier!

1000 REM FACTOR - PAT HALL, JAN '84
1010 REM
1020 GOB LIB 1120 : REM DEFINE SPRIT ES
1030 GOSUB 1610 a REM STORE PRIMES
1040 GOSUB 1700 s REM SET UP DISPLAY
1030 GOSUB 1880 a REM TEST RO UT INE

20

Chapter 1 Starting with Maths

1.060 80SUB 21.60 s REM FLY PLANE
I. 070 GOTO 1.050
.1.080 END
1090 REM
II. 00 REM DEFINE SPRITES

11.1.0 REM BEGI NNI NG OF 6567 VID EO CHIP

11.20 VC - 53248

11.30 REM PLANE, SPRITE 0
1140 REM SET POINTER FOR SPRITE 0

11.50 POKE 2040, 13

1.1.60 REM READ DATA FOR SPRITE 0
1170 FOR I. = 0 TO 1.9
1180 POKE 832 + I, 0

11.90 NEXT I

1.200 FOR I = 20 TO 62

1.210 READ N ; POKE 832 + I, N

1.220 NEXT I
1230 REM BOMB, SPRITE 1.
1240 REM SET PO IN TER FOR SPRITE 1

1.250 POKE 2041, 1.4

1.260 REM READ DATA FOR SPRITE 1
1270 FOR I ■ 0 TO 39
1280 POKE 896 + I,

0

1.290 NEXT I

1.300 FOR I = 40 TO 62

1.310 READ N s POKE 896 + I, N

1.320 NEXT I

1330 REM FLASH, SPRITE 2

1340 REM SET POINTE R FOR SPRITE 2

1350 POKE 2042, 15

1.360 FOR I = 0 TO 39

1370 PO KE 960 + I, 0

1.380 NEXT I

1390 FOR I = 40 TO 62

1.400 READ N s POKE 960 + I, N

1410 NEXT I.

1420 REM ENLARGE SP RI TES 0 AND I.

1430 REM X--DIEECTION

1.440 POKE VC + 29, 5

1450 REM Y- DIRECTION

1460 POKE VC + 23, 5

1470 REM SELECT COLOUR

1480 REM BL UE PLANE
1490 POKE VC + 39, 6

21

Programming for Education on the Commodore 64

.1.500 REM BLACK BOMB

1.510 POKE VC + 40, 0
1520 REM BROWN FLASH
1530 POKE VC + 41, 9
1540 REM LOCATE FLASH ON SCREEN
1550 POKE VC + 4, 165 ; REM X-COORD
1560 POKE. VC + 5, 143 5 REM Y-COORD

1.570 RETURN
1580 REM
1590 REM STORE PRIMES
1600 REM DIMENS ION PRIMES' ARRAY, PN
1610 DIM P N ( 29 )
1620 REM READ PRIME NUMB ERS FROM DATA
1630 FOR I = 1 TO 29
1640 READ N : P N ( I > - N
1650 NEXT 1
1660 RETURN
1670 REM

1.680 REM SET UP DISPLAY

1690 REM CYAN BORDER

1700 POKE 53280, 3

1710 REM CYAN BACKGROUND

1720 POKE 53281, 3

1730 REM CL EAR THE SCREEN

1740 PR I NT " I SHI FT / CLR / HOME li "
1750 REM DRAW DESERT LANDSCAPE
1760 FOR I = 0 TO 280 STEP 40
1770 FOR J = 0 TO 39
1780 REM POKE COLOUR TO SCREEN
1790 POKE 5597 6 + I + J,

8

1800 REM POKE. CHAR ACT ER TO SCREEN
1810 POKE 1704 + I + J , 160
1820 NEXT J
1830 NEXT I
1840 RETURN
1850 REM
1860 REM TEST ROUTINE
1870 REM SELECT NUMBER
1880 TN = INTI R N D < 1 ) * 70 ) + 30
1890 REM CHECK. TARGET IS NOT PR IM E
1900 N = TN : GQSUB 2080

1.910 IF PF - 1. THEN 1.880

1.920 X = 19 : Y = 16 s GOSUB 2520

1.930 PRINT TN

22

Chapter 1 Starting with Maths

1940 X = 8 : Y = 0 : 6QSUB 2520

1950 PRINT "TYPE A FACTOR OF" TN

1960 X = 30 : GO SUB 2520

1970 PRINT "

1980 GOSUB 2520

1990 INPUT FT
2000 IF A S C ( FT) < 49 THEN 19600
2010 IF A S C ( FT) > 57 THEN 1960
2020 F = V A L ( FT)
2030 IF INT(TN/ F) <> TN/F THEN 1960
2040 IF F = 1 OR F = TN THEN 1960
2050 RETURN
2060 REM
2070 REM PRIME CHECK
2080 PF = 0
2090 FOR I = 1 TO 29
2100 IF N » PN( I ) THEN PF = 1
2110 NEXT I
2120 RETURN
2130 REM
2140 REM FLY PLANE
2150 REM SWITCH ON PLANE, SPRIT E 0
2160 POKE VC + 21, 1
2170 REM PLANE ON RIGHT HAND SIDE
2180 REM SO SET MOST SIGNI FICANT BIT
2190 POKE VC + 16, 1
2200 FOR I = 50 TO 0 STEP -1
2210 REM ADJUST X-COORD OF PLANE
2220 POKE VC, I
2230 REM LEAVE Y-COOR D C ONSTANT
2240 POKE. VC + 1 , 80
2250 NEXT I
2260 REM CON TINUE FL IGHT ON LEFT
2270 REM TURN OFF MOST S IGN IFICANT BIT
2280 POKE VC + 16, 0
2290 REM DROP BOMB, SWITCH ON SPRITE 1
2300 POKE VC + 21, 3
2310 FOR I = 255 TO 189 STEP -1
2320 REM ADJUST X-COORD OF PLANE
2330 POKE VC, I
2340 REM LEAV E Y-CO ORD CONSTANT
2350 POKE VC + 1, 80
2360 REM BOMB HAS SAME X-COORD AS PLANE
2370 POKE VC + 2, I

23

Programming for Education on the Commodore 64

2380 REM Y-COORD OF BOMB
2390 POKE VC + 3, 355 - I
2400 NEXT I
2410 REM SWI TCH BOMB OFF, FLASH ON
2428 PO KE VC +21, 5
2430 REM FLY PLANE ON
2440 FOR I = 188 TO 0 STEP -1
2450 POKE V C , I : POKE VC + 1, 80
2460 NEXT I
2470 REM SWI TCH OFF PLANE AND FLASH
2488 POKE VC + 21, 0
2490 RETURN
2500 REM
2510 REM PRINT TAB ROUT INE
2520 POKE 782, X : POKE 781, Y

2538 SYS 65520
2540 RETURN

2550 REM
2560 REM DATA FOR PLANE, SPRITE 0
2570 REM
2580 DATA 7, 0, 0, 15, 3, 128, 30, 4
2590 DATA 64, 60, 127, 255, 252, 255
2608 DATA 255, 255, 255, 255, 255, 1
2610 DATA 255, 254, 3, 255, 224, 0,

CN IN

in

2620 DATA 224, 0, 63, 224, 0, 15, 240
2630 DATA 0, 3, 252, 0, 0, 254, 0,0, 63
2640 REM
2650 REM DATA FOR BOMB, SPRITE 1
2660 REM
2670 DATA 4, 8 , 0, 6, 0, 0, 7, 0, 0
2680 DATA 24, 0, 0, 112, 0, 0, 240, 0
2698 DATA 0, 240, 0, 0, 224, 0
2700 REM
2710 REM DATA FOR FLASH, SPRITE 2
2720 REM
2730 DATA 65, 0, 0, 42, 0, 1, 0, 64, 0
2748 DATA 136, 128, 4, 65, 16, 2, 42
2750 DATA 32, 1, 0, 64, 0, 227, 128
2760 REM
2770 REM DATA FOR PRIME NUMBERS
2780 REM
2790 DATA 2, 3, 5, 7, 11, 13, 17, 19
2800 DATA 23, 29, 31, 37, 41, 43, 47

24

Chapter 1 Starting with Maths

2810 DATA 53, 57, 59, 61, 67, 71, 73
2820 DATA 79, 83, 87, 89, 91, 93, 97

REA D Y .

Commentary

Factor is controlled by lines 1020-1070.

The first subroutine, called by line 1020 of the control module, defines
three sprites used in the program. Sprite 0 is a plane, sprite 1 is the bomb
that it drops and sprite 2 is the flash of the resultant explosion when the
plane successfully hits its target number. Each of the three sprites is defined
in a similar way.

The diagram shows how the plane has been drawn on a rectangular grid
of 21 rows and 24 columns. Each block of eight horizontal squares has
been coded as a binary number and then stored in a special area of memory
reserved by line 1150. Usually after a sprite has been designed and calcu
lated as a set of 63 numbers, these are held inside a program as DATA.
However, in the case of the plane sprite it can be seen from the diagram that
the first twenty blocks of eight squares have not been filled in at all. Thus
the numbers corresponding to these blocks are each zero.

It is much easier to place these values into memory with the simple FOR

.. .NEXT loop between lines 1170-1190 than to store them as DATA.

The remaining numbers for the sprite are, however, READ from the

DATA lines. The values for sprite 0 are held at locations starting at 832.
The two other sprites are stored at locations starting at 896 and 960. Each
time, the ‘sprite pointer’ is set to indicate where in memory the sprite data is
to be found.

The rest of the routine then attends to other sprite parameters. These are

all done in terms of the number VC defined at line 1120. This is the starting
location of the video chip, which handles all the sprite manipulation.

POKE VC+ 29, for example, is the location which controls the size of a

sprite in the horizontal, x, direction. POKEing the sprite number to

VC + 29 will cause it to be stretched sideways. In this program, both sprite

0 and sprite 2 need to be expanded and so the value 5 is POKEd. This is the

sum of 1 (sprite 0) and 4 (sprite 2). In a similar way, the colour and location

of sprites on the screen are all controlled with reference to this important

location VC.

In the operation of the program, it is necessary to be able to identify prime

numbers. Primes are held, again as lines of DATA, and READ into the PN

array by the routine between lines 1590-1660.

25

Programming for Education on the Commodore 64

Diagram A

The screen display is built up by the routine between lines 1680-1840. As in
the program Bingo, the screen is controlled by directly addressing the
screen and colour maps. For example, the bottom section of the screen is
turned into a desert by the nested loops between lines 1760-1830.

The test routine from lines 1860-2120 present a target number which the
child has to attempt to bomb. This can only be done by typing in a correct
factor. The input routine is error-trapped to prevent the number itself, or

1, or non-numeric values, from being accepted. The target number itself is
carefully tested by the separate subroutine to make sure that a prime
number is not set. This is achieved by using the array of prime numbers set
up earlier in the program.

The routine from 2140-2500 flies the plane over the desert and bombs the
number if a correct factor has been typed. The REMs present in this
routine indicate each stage of the flight. Note how the location VC + 16 has
been set at line 2190 to allow the flight across the righthand side of the
screen.

26

CHAPTER 2

Small is Beautiful

Short programs and efficiency — Missing: find the numbers —

ordering numbers — Series: maths as an introduction to strategy —

simplicity in program structure — Number: a program to find a

hidden number — using graphics to brighten up simple ideas —

Firework: a program to test general numerical skills — the problems

involved in learning fractions — Fraction: a program to help with
numerators and denominators.

Although it has been pointed out that exciting displays do not turn a
mediocre program into a good one, there is no doubt that some programs
benefit from interesting graphics.

At the beginning of this chapter, we shall show you some short programs
in which the fast calculating power of your 64 is used, rather than its
graphic ability. Towards the end, some of these ideas are put into a more
advanced program that includes graphics.

Firstly though, an indication of simple ways in which the computer can

do tasks faster and more efficiently than humans.

A question of format

In the last chapter, there was a table test program that used the computer to
generate the questions. The same idea can be used with any sort of maths

problem. One difficulty that many children in the early primary years

experience is that of coping with problems posed in an unfamiliar way. If a
sum says

15 - ? = 7

then it is likely to pose more problems than one that says

15-7 = ?

The following program chooses 10 problems at random using this format.

27

Programming for Education on the Commodore 64

Missing

1 REM *** MISSI NG NUMBERS ***
20 REM
30 REM *** A.J.S. 1/7/83 *•**
40 REM
50 S=0s PR INT"[S H I FT/CL R /HOME 3"s PRINT
60 FOR N - 1 TO 10
70 A = INT < R N D (0)*100)
80 B = IN T (RN D (0)*100)
90 IF B>A THEN 70

100 C = A - B

110 PRINT N A ;" -••• ? =";B

120 PRINT

130 INPUT "MISSING NUMB ER IS";GU ESS

140 IF GUESS = C THEN PRINT "OK":S=S+1

150 IF GUESS <>C THEN PRINT "NO";C

160 FOR COUNT=l TO 500 : NEXT COUNT

170 PRINT "CS HIFT /CLR/ H OME3 "
180 NEXT N

190 PRINT"YOUR SCORE WAS"S"O UT OF 10"

REA D Y m

Line 50 sets the score to zero and clears the screen. Line 60 starts the loop to
ask 10 problems.

Lines 70 and 80 choose random whole numbers between 0 and 99, and line
90 checks that B is not greater than A.

Line 100 calculates the answer. Line 110 sets out the question line. The
semicolons in this line are not essential, as they are in an INPUT line, eg
line 130.

Line 120, a simple PRINT statement, is an easy way of missing
a line.

Line 130 requires an input, GUESS. Lines 140 and 150 check GUESS and
compare it with the correct answer, C. If it is the same, the score is
increased by one.

28

Chapter 2 Small is Beautiful

Line 160 shows a simple way of introducing a pause. The empty
FOR.. . NEXT loop counts up from 1 to 500, and then allows the program
to continue.

Line 170 clears the screen. Line 190 prints the score, S.

Everything in order

Sequences and series of numbers sometimes take a long time before the
idea is grasped. The next program shows how the computer can generate a
series of numbers in a particular range. Although not an elaborate pro
gram, it will generate sequences and mark the responses all day without
getting tired.

The particular sequence chosen is one that increases by the same amount

each time, eg

4 8 12 16 20 24 etc.

It is quite easy to change the program so that it chooses numbers where the
increment alters by a set amount, eg

1 2 4 7 11 15 etc.

or one that generates squares such as

1 4 9 16 25 36 etc.

Series

10 REM *** SERIES GUESSER ***

20 REM
30 REM *** A.J.S. 5/7/83 ***
40 REM
50 PRINT" CSHIFT/CLR/HOMEIt " : PRINT
60 PRINT "SERIES"
65 PRINT;S = 0
70 FOR N = 1 TO 10
75 PRINT "QU ESTION"N
80 A -I N T (R N D (0)* 2 6 )

90 I NCR = I NT (F;NB ( 0) * 11)

100 PRINT A;

110 FOR X = 1 TO 4

120 PRINT A + (INCR * X);

29

Programming for Education on the Commodore 64

130 NEXT X
140 PRINT
150 B = A + (INCR * X)
160 INPUT "WHAT IB THE NEXT NU MBER";G
170 IF G = B THEN PRINT"OK":S-B+l
180 IF G O B THEN PR I N T " NO "B
190 NEXT N

200 PRINT "YOU SCO RED"S "OUT OF 10"

READ Y .

Commentary

Line 50 clears the screen. Line 65 sets the score to 0 at the start.

Line 70 begins the loop to generate 10 questions. Line 80 chooses A, the
start of the series, at random. Line 90 chooses the size of the step or incre
ment between each number, INCR. Line 100 prints the first number in the
sequence.

Lines 110 to 130 contain a loop to generate the next four numbers in the
series. Each number is bigger by the amount INCR.

Line 150 relies on the fact that the FOR... NEXT loop counters contain a
value one higher than the last count of the loop, ie 5, to set B equal to the
next number in the sequence. Line 160 asks for an input, G.

Lines 170 and 180 compare G with the correct answer, B, and print OK or
NO, as well as increasing the score if necessary.

Line 200 prints the final score.

Logical guessing

There is a game that you can play using the blackboard, a piece of paper, or
just your memory. It is the familiar one of ‘I am thinking of a number —
ask me any question about it you like, but I can only reply using yes or no.’
Faced with this problem for the first time, the child may be inclined to
guess. If he or she realises that the number can be anything under (say)

1000, it is not long before it is appreciated that the task is difficult, and that
some sort of logical strategy must be employed.

30

Chapter 2 Small is Beautiful

In a classroom situation, the class usually divides up into ‘guessers,

‘hypothesises’ and ‘pseudo-hypothesisers’. Guessers do just that.

Hypothesisers try to reduce the number of possible choices by asking such
questions as ‘is it an even number’ or ‘is it less then 500’. Pseudo-hypothe
sisers are more subtle than the guessers. If the response ‘no’ is received to
the question ‘is the number less than 500’, then the sort of question they
will ask is ‘is it more than 500’. It sometimes seems a big hurdle to jump
before this type of child realises that a ‘no’ response to a question provides
as much information as a ‘yes’.

This sort of game is a useful activity as it can improve mental skills
including memory and visualisation of a sort of internal number line. It
also helps develop logical questioning and inquiry strategies. You can
probably see that the most logical strategy to follow is to divide the answer
approximately by two.

A typical series of questions may go as follows:

Number is 242.

Is it

larger than 500?

Is it

larger than 250?

Is it

larger than 125?

Is it

larger than 190? Yes.

Is it

larger than 230?

Is it

larger than 240? Yes.

Is it

larger than 245?

Is it

larger than 243?

Is it

larger than 241?

Is it

242? Yes.

No.
No.
Yes.

Yes.

No.
No.
Yes.

Using this binary chopping method, it is always possible to reach the
number without guessing in less than ten attempts — two raised to the
power of ten is, of course, 1024. Most older children will adopt this
method, or one similar, until they get fairly close and then guess. It is not
envisaged that they will actually be calculating the odds on a correct guess,
although at this level it does resemble gambling!

A computer can choose the number, select correct responses and give the
total number of attempts at the end. In this way, a teacher or parent can be
relieved of the task of administering this game to children, and the pro
gram allows an individual or group approach. For the child who finds it
difficult to acquire a good strategy, it can provide as much practice as is
necessary.

There are no interesting displays, no exciting sounds, and the program
has been made as simple as possible to show how even short programs can
have their point.

31

Programming for Education on the Commodore 64

Number

10 REM ** NUM BER Gl.JESSER **
20 REM ** A.J.S. 1/4/82 * *
30 REM
40 P 0 K E 5 3 2 8 1,1:REM BACKGROU ND WHITE
50 PR IN T "ISHIFT/CLR/HO M E 1"
60 5C-0
70 BO=0
80 PRINT" I. WILL THINK OF A NUMBER. ";
90 P RINT"YOU MUST TRY"

100 PRIN T"TO GUESS IT IN AS FEW GOES ";

110 PR INT"AS YOU CAN."

120 PR INT"CHOO SE A TOP LIMIT ";

130 INPUT"FOR YOUR NUMBER";T P

140 N = I N T(R N D <1)* T P )

150 P RINT" THE NUMB ER LIES BETWEEN ";

160 PRINTED;" AND ";TP

170 SO=SC+l

180 PR INT"E NTER GUESS NO.";SC;" ";

190 INPUT GS
200 IF GS-N THEN GOTO300
210 IF GS>N THEN TP=GS
220 IF 6S<N THEN B0-G3
230 G O TO 150
240 REM
300 PRINT"YO U GOT IT IN ";SC;" GOES"
310 PRINT"PR ESS SP AC E BAR TO GO AGAIN"
320 GET Zf
330 IF Z*<>" " THEN 320

340 GOTO50

READY.

Commentary

Line 40 sets the background colour to white. Up to this point, you have

probably been putting up with the light blue background that appears
when you switch on. POKEing this location in memory with a number

from zero to 16 sets the background colour.

Line 60 initialises the score, SC. Line 70 sets the bottom limit for the

number to zero.

32

Chapter 2 Small is Beautiful

Lines 80 to 120 contain the instructions.

Line 130 allows the user to set the upper limit for the number. Line 140

chooses the number to be guessed.

Lines 180 and 190 allow the input of a guess.

Lines 200 to 220 check the guess, GS, against the chosen number, N. If the

guess is larger than the number, then the guess becomes the new upper

limit; and if the guess is smaller than the number, the guess becomes the

new bottom limit.

Although it is not so easy to see, there is a loop between lines 150 and 230.
This loop is negotiated each time a number is guessed, until the correct
answer is given. This causes an exit in line 200. 64 BASIC only supports a
FO R.. .NEXT loop, and this entails knowing how many times you will

pass through it, which in this program, of course, you don’t.

Lines 300 and 310 print the number of guesses, SC.

Line 320 contains the words GET Z$. This waits until a key is pressed, and
then checks the input in line 330. If the key is anything except the space bar,
the program repeats line 320.

Line 340 sends the program back to the start.

Firework

The next program, Firework, is also based on a simple idea — offering

examples of the four rules (add, subtract, multiply and divide). The incen

tive to do well here is the impressive display after five correct answers.

Each of the graphic routines is held in a module, and may be adapted to
your own use or copied directly into a different program. Full notes on how
the effects are achieved are to be found at the end of the program.

1000 HEM FIREWORK

- PAT HALL, JAN '84

1010 REM

1020 GOSUB 1110 :

1030 GOSUB 1520 :
1040 GOSUB 1730 :
1050 GOSUB 2040 ;

REM DE FINE SPRITES
REM SET UP DISPLAY
REM TEST ROUTINE

REM LA UNCH RO CKET
1060 GOTO 1030
1070 END

33

Programming for Education on the Commodore 64

.1.080 REM

1.090 REM DEFINE SPRITES

1.100 REM BEGI NNI NG OF 6587 VIDEO CHIP
1110 VC « 53248
1120 REM ROCKET, SPRITE 0

1.130 REM SET P OINTER FOR SPRITE 0
1140 POKE 2040, 13
1150 REM READ DATA FOR SPRITE 0
1160 FOR I = 0 TO 8
1170 READ N : POKE 832 + I, N
1180 NEXT I
1190 FOR 1 - 9 TO 51 STEP 3
1200 POKE 832 + I, 0

12.1.0 POKE 833 + I, 1.27
1220 POKE 834 + I, 0
1230 NEXT I
1240 FOR I ■ 54 TO 62

1.250 READ N : POKE 832 + 1, N
1260 NEXT I

1.270 REM EXHAUST, SPRITE 1
1280 REM SET POIN TE R FOR SPRITE 1

1.290 POKE 2041 , 3.4
1300 REM READ DATA FOR SPRITE 1
1310 FOR I = 0 TO 62
1320 READ N : POKE 896 + I, N

1.330 NEXT I
1340 REM MOON, SPRITE 2

1.350 REM SET POINTER FOR SPRITE 2
1360 POKE 2042, 15
1370 REM READ DATA FOR SPRITE 2
1380 FOR I = 0 TO 62
1390
1400

1.41.0 REM
1420
1430
1440 POKE
1450
1460 POKE

READ N : POKE 960 •+■

I ,

NEXT I

ENLARGE SPRITES IN

POKE

VC + 29, 5

REM ENLARGE SPRITES IN Y

VC + 23, 5

SELECT COLOUR

REM

VC + 39, 1

N

X DIREC TION

DIRECT ION

.1.470 POKE VC + 40, 2
1480

POKE

VC + 41 , 7

1490 RETURN

1500 REM

1510 REM BLUE SKY

34

Chapter 2 Small is Beautiful

1520 POKE 53280, 6 : POKE 53281, 6
1530 PR I NT " t: SHI FT / CL..R / HOME 1 "
1540 REM DRAW GR ASS
1550 C - 5 s REM SELECT GREEN
1560 FOR 1 = 0 TO 160 STEP 40
1570 FOR J = 0 TO 39
.1580 L = 1824 + I + J
1590 GOSUB 2900
1600 NEXT J
1610 NEXT I
1620 REM PLACE ROCKET ON GRASS
1630 REM HORIZO NTAL POSITION
.1.640 POKE VC, 165
1650 REM VERTIC AL POSITI ON
1660 POKE VC + 1 , 190
1670 REM SWITCH ON ROCKET, SPRITE 0
1680 POKE VC + 21, 1
1690 PRINT C H R T ( 5 )
1700 RETURN
1710 REM
1720 REM TEST RO UT INE
1730 S = 0
1740 P = 10 : REM SET PAUSE
1750 X = 14 s Y = 0 : GOSUB 2700
1760 PRINT "<< FIRE WO RK >>"
1770 A = IN T ( R N D ( 1 ) * 96 ) + 5
1780 B = I NT-: RND< 1 ) * A )
.1790 REM PREVENT TOO EASY QU ES TI ONS
1800 IF B < 11 THEN 1770
1810 GOSUB 2940 : REM PAUSE
1828 X = 8 : Y = 2 : GOSUB 2700
1830 PRINT "WHAT IS " A B
1840 X = 30 s Y = 2 ; GOSUB 2700
1850 PRINT "
1860 GOSUB 2700
1870 INPUT C*
1880 IF A S C ( C$)< 49 THEN 1840
1890 IF A S C ( C*> > 57 THEN 1840
1900 C = VAI.. < C$>
1910 IF C = A - B THEN 1950
1920 GOSUB 2700 ; PRINT " NO " A B
1930 GOTO 1770
1940 REM INCREASE SCORE
1950 S = S + 1 IF S < 5 THEN 1770

35

Programming for Education on the Commodore 64

.1.960 REM CLEAR TOP OF SCREEN
.1970 X « 14 : Y » 0 s GOSUB 2700
1980 PRINT "
1990 X » 8 : Y » 2 s GOSUB 2700

2000 PRIN T "
2018 RETU RN
2020 REM

2030 REM LA UNCH ROCKET

2040 P - 1 s REM ADJUST PAUSE

2050 REM BNITCH ON EXHAUST, SPRIT E 1

2060 POKE VC + 21, 3

2070 SD - 1 : GOSUB 2770 : REM SOUND
2080 FOR I == 190 TO 120 STEP -1
2090 REM KEEP X COORDINA TE CONSTANT
2100 POKE VC, 165
2110 REM A DJUST Y COORDI NATE
2120 POKE VC + 1 , I
2130 REM PLACE EXHAUS T
2140 IF I > 160 THEN 2230
2150 REM E NLARGE EXHAUST
2160 REM ADJUST IX X DIRECTIO N
2170 POKE VC •+• 23, 7
2180 REM A DJUST IN Y DI RE CTION
2190 POKE VC + 29, 7
2200 REM X COOR DIN ATE FOR LARGE EXHAUS T
2210 POKE VC + 2, 165
2220 GOTO 2240
2230 POKE VC + 2, 177
2240 POKE VC + 3, I + 43
2250 GOSUB 2940 : REM PAUS E
2260 NEXT I
2270 REM GROUND SLIPS AWAY
2280 C = 6 : REM SELECT BLUE
2290 FOR 1 = 0 TO 160 STEP 40
2300 FOR J = 0 TO 39
2310 L = 1824 + I *• J
2320 GO SUB 2900
2330 NEXT J
2340 NEXT I
2350 P = 5 s GOSUB 2940 : REM PAUSE
2360 REM BLACK SKY
2370 POKE 53280, 0 : POKE 53281, 0
2380 PR I NT " I! SHI FT / CLR / HOME 1 "
2390 P = 10 : GOSUB .2940 s REM PAUSE

36

Chapter2 Small is Beautiful

2400

241.0

2420
2430
2440
2450
2460
2470
2480
2490

2500
2510
2520
2530
2540
2550
2560
2570
2580
2590

2600
2610
2620
2630
2640
2650
2660
2670
2680
2690
2700

2710

2720
2730

2740
2750
2760
2770
2780
2790
2800
2810
2820

REM MOON ARREARS
POKE VC + 21, 7
REM MOVE MOOM DOWN SCRE EN
P = .5 s REM ADJUST PAUSE
FOR I «

8 TO 250

POKE VC + 4, 30
POKE VC + 5, I
(30SUB 2940 : REM PAUSE
NEXT I.
P = 5 : (30SUB
SD = 0 s GQSUB

940 : REM PAUSE

2770 : REM SOUND
REM STARBURST
REM SWITCH OFF

ROCKET, SPRITE 0

POKE VC -I- 21, 0

FOR I = 1 TO 8

L = 1524 + I :
L. * 1524 - I s
L 1524 -i- I *
L ■--- 1524 - I *

I.... = 1524 + I +

L ~ 1524 + I -
L. = 1524 I +
L •= 1524 - I

GOSUB 2980

GOSUB 2980

40 ; GOSUB 2980

40 s GOSUB 2980

I * 40 s GOSUB 2980
I * 40 : GOSUB 2980

I * 40 : GOSUB 2980

I * 40 : GQSUB 2980
NEXT I
REM LIGHT UP SK

Y

POKE 53280, 3 : POKE 53281, 3
P -- 50 : GOSU B 2940 : REM PAUSE
RETURN
REM
REM PRINT TAB RO UT INE
POKE 782, X s POKE 781, Y
SYS 65520
RETURN
REM
REM SOUND EFFECT
REM SD = 1, SOUND ON

REM SD = 0, SO UND OFF

IF SD = 0 THEN 2840
POKE 54296, 15
POKE 54277, 129
POKE 54278, 129
POKE 54276, 129
POKE 54273, 10

POKE 54272,

60

37

Programming for Education on the Commodore 64

2830 GOTO 2870
2840 POKE 54277, 0
2850 POKE 54278, 0
2880 POKE 54276, 0
2870 RETURN

2880 REM
2890 REM PLOT CHAR ACTER SPACE
2900 POKE L + 54272, C ; POKE L, 160

2910 RE TU RN
2920 REM
2930 REM PAUSE

2940 FOR T = 1 TO P * 30 : NEXT T
2950 RETURN

2960 REM

2970 REM PLOT STAR

2980 C = IN T ( RND < 1 ) * 7 ) + 1

2990 POKE L + 54272, C : POKE L, 42

3000 RE TU RN

3010 REM

3020 REM DATA FOR ROCKET, SPRITE 0

3030 REM

3040 DATA 0, 8 , 0, 0, 28, 0, 0, 62, 0

3050 DATA 0, 8 , 0, 0, 28, 0, 0, 62, 0

3060 REM

3070

3080

3090

3100

3110

3 1 2 0

3130

3140

3150

3160

3170

3180

3190

3200

3210

3220

REM DATA FOR EXHAUST, SPRITE 1
REM
DATA 0, 8, 0, 0, 8 , 0, 0, 24, 0
DATA 0, 60, 0, 0, 118, 0, 0, 231
DATA 0, 1, 227, 128, 1, 225, 192
DATA 1, 225, 224, 0, 241, 224, 0

DATA 249, 240, 0, 125, 240, 0, 29
DATA 240, 0, 15, 224, 0, 7, 192

DATA 0, 7, 128, 0, 7, 128, 0, 7, 0
DATA 0, 14, 0, 0, 12, 0, 0, 16, 0
REM
REM DATA FOR MOON, SPRITE 2
REM
DATA 0, 30, 0, 0, 7, 128, 0, 3
DATA 224, 0, 1, 240, 0, 0, 248, 0
DATA 0, 252, 0, 0, 126, 0, 0, 126
DATA 0, 0, 127, 0, 0, 127, 0, 0

3240

3250

DATA 127, 0, 0, 127, 0, 0, 127,
DATA 0, 126, 0, 0, 126, 0, 0, 25

f-0 Q

38

Chapter 2 Small is Beautiful

3260 DATA 0, 0, 248, 0, 1, 240, 0, 3
3270 DATA 224, 0, 7, 128, 0, 30, 0

READ Y .

Commentary

The control module for Firework is formed by the lines 1020-1060. It can
be seen that the program is in an overall loop and so RUN/STOP has to be

used to escape from it.
The first routine of the program defines three sprites. First the value of VC

is initialised by line 1110. Then the rocket, its exhaust and the Moon are
defined in turn as sprites 0-2 . The three diagrams show each of the sprites
in detail. It can be seen that the major part of the rocket is a very repetitive

shape and this pattern is reflected in the way that the corresponding sprite
data is built up by the use of the F O R .. .NEXT loop from lines

1190-1230. The other two sprites are built up instead simply from the

DATA stored at the end of the program. Lines 1410-1480 then select the
size and colour of the sprites.

Lines 1510-1690 colour the screen blue and place grass at the bottom. The
rocket is located on the grass by POKEing the two locations VC and
V C +1, which control its horizontal and vertical location on the screen.
Finally the rocket is made to appear by POKEing its sprite number, 1, to
VC+ 21. This is the location which controls whether a particular sprite
appears on the screen or not. Line 1690 selects white text for the subsequent
test routine.

The test given to the child is simple subtraction of numbers. Line 1770
chooses A to be a number less than 100. Line 1780 then multiplies A by a
random decimal number and takes the integral part. In this way, it is
ensured that the number being subtracted is not larger than the one it is
being subtracted from. Line 1800 then prevents the calculations from
being too easy. Again extensive use is made of a PRINT TAB subroutine to
allow the screen to be neatly arranged. Lines 1840-1890 stop letters being
accepted as an input. The variable S keeps a record of the child’s success
and governs exit from the test to the reward routine at line 1950.

Lines 2030-2670 control the flight of the rocket up into the sky. Here the
sprites allow easy animation. An increased sense of upward motion is
attempted by removing the ground between lines 2280-2340 and by
moving the Moon downwards in the loop 2440—2480. The sound of the

rocket is created by the separate routine between lines 2740-2870 and con

trolled by the value of the flag SD. The loop from 2540-2630 uses another

subroutine to place a starburst on the screen.

39

Programming for Education on the Commodore 64

40

Chapter 2 Small is Beautiful

41

Programming for Education on the Commodore 64

Diagram D

42

Chapter 2 Small is Beautiful

Fraction

There is no doubt that in the whole of maths teaching, there is no topic so

off-putting to children, parents and teachers alike as that of fractions.

Children of seven and eight often have an intuitive grasp of halves and

quarters, but the notation of vulgar fractions is unfamiliar and the terms

numerator and denominator are awkward in themselves. Recent surveys,
such as the Cockroft Report (1982), have implied that work should concen
trate on decimal fractions at least until the upper end of primary schools.

This does not mean that the idea of fractions can go out of the window.
Children need a lot of practical experience in dividing objects up into
equal-sized parts before they understand fractional concepts. It is usually
in the recognition of what a fraction stands for, and in the manipulation of
its parts, that problems occur. In this chapter, we have attempted to tackle
this problem in different ways.

Fraction displays a rectangle, representing the whole object; it then
colours in a particular fraction and asks the child to input the numerator
and denominator. These terms are used on the screen and there is no doubt
about which is which.

As an aid to knowing how to express the fraction, ie whether j or { is
required, the whole rectangle is divided up into the same number of parts as
the denominator. For instance, if \ is required, the rectangle divides into six
clearly-defined sections, and two of these are coloured in. Should the child
make an incorrect input, there is a routine to show how the fraction is built
up. If the child is successful, the examples become progressively more dif
ficult, whereas those for a child with difficulties remain simple.

.1.000 REM FRACT ION

1010 REM

1020 GOSUB 1200 :

1030 GOSIJB 1170 :
1040 GOSUB 1360 :
1050 GOSUB 2010 s
1060 GOTO 1030
1070 END
1080 REM
1090

1100

1110

1120

.1.130
1140
1150
1160

REM INITIALISATION

REM SCORE AND NUMBER AT TEMPTED
S = 0 : G - 0

REM LEVEL OF DIFFICULTY
DF = 1
RETURN
REM
REM SELECT FR AC TION

- PAT HALL, JAN '84

REM INITIALISATION
REM SELECT F RACTI ON
REM DRAW D IAGRAM
REM REQUEST ANSWER

43

Programming for Education on the Commodore 64

I N K RNIK 1 )

1170
1180 N =
1190 IF

1200
1210 W «
1220

1230 IF
1240 IF D < 8 THEN W =
1250
1260 IF
1270
1280

1290 IF D < 3 THEN W -
1300 REM'
1310 LD
1320 RETURN
1330 REM
1340 REM DRAW DIAGRAM
1350 REM WHIT E SCRE EN
1360 POKE 53280, 1 : POKE 53281, 1
1370 PRINT "CSHIFT/CLR/HOME'J"
1380 REM PRINT TITLE
1390 PRINT C H R T ( 144 )
1400 X = 13 : Y = 0 s'GOSUB 1950
1410 PRINT " « FRACTI ON >>"
1420 PRINT CHR$< 30 )
1430 X = 12 : Y = 2. : GOSUB 1950

1440 PRINT "SCORE: " S " / " G
1450 PRINT C H R T ( 144 )
1460 REM DRAW D DIVISI ONS
1470 FOR I = 1 TO D
1480 REM LOCATE TOP LEFT OF DIVISION
1490 LD = LD + W + 1
1500 REM PLOT TOP AND BOTTOM OUTLINE
1510 C = 0 : REM SELE CT BLACK
1520 FOR J = 0 TO W
1530 L = LD + J
1540 GOSUB 1920
1550 L - LD + 560 + J
1560 GOSUB 1920
1570 NEXT J
1580 REM SOUND EFFECT
1590 POKE 54296, 15 : POKE 54277, 129
1600 POKE 54278, 129 : POKE 54276, 17

D =

INT < R N D ( 1 )

N < 1 THEN 1180

REM1 SELECT WIDTH

1

D < 13 THEN W

IF

D < 10 THEN W

IF

D < 7 THEN W =■--
D < 6 THEN W =

IF

D < 5 THEN W =
D < 4 THEN W =

IF

1 LOC ATE TOP LEFT OF

« 1203 - D * (

* DF
* D )

OF DI VISIONS

_

= 3

4
5

'tf

8

11

17

W + 1

) + 2

DIAGRAM

) / 2

44

Chapter 2 Small is Beautiful

1610 POKE 5 4 2 7 3 , 68 : POKE 54272, 149
1620 FOR T = 1 TO 90 : NEXT T
1630 POKE 54277, 0 r. POKE 54278, 0
1640 POKE 54276, 0
1650 REM LEFT HAND EDGE
1660 FOR J = 40 TO 520 STEP 40
1670 L = LD + J

1680 GOSUB 1920
1690 NEXT J
1700 REM COLOUR IN DIVISION
1710 REM COL OUR NU MERATOR GR EE N

1720 C = 5

1730 REM COLOUR OTHER DIVISION S YELLOW

1740 IF I > N THEN C “ 7

1750 FOR J - 40 TO 520 STEP 40

1760 FOR K. = 1 TO W

1770 L = LD + J + K

1780 GOSUB 1920

1790 NEXT K.

1800 NEXT J

1810 NEXT I

1820 REM FINAL RIGHT HAND EDGE

.1830 C = 0 ; REM SELECT BLACK

1840 LD = LD + w + 1

1850 FOR I = 0 TO 560 STEP 40

1860 1... = LD + I

1870 GOSUB 1920

1880 NEXT I

1890 RETURN

1900 REM

1910 REM PLOT CHARACTE R SPACE

1920 POKE L + 54272, C : POKE L, 160

1930 RETURN

1940 REM PRINT TAB ROUTIN E

1950 POKE 782, X : POKE 781, Y

1960 SYS 65520

1970 RETURN

1980 REM

1990 REM REQUEST ANSWER
2000 REM INCREMENT NUMBER ATTEMPT ED

2 0 1 0 G = G + 1

2020 REM REQUEST ANSWER
2030 X = 8 s Y = 20 : GOSUB 1950

2040 PRINT "WHAT FRACT ION IS GREEN ?"

45

Programming for Education on the Commodore 64

2050 Y = 22 : G OSUB 1950
2060 PRINT "TYPE NUMERATOR;-"

2070 XA = 22 : GOSUB 2200

2080 Ml = AN

2090 X = 8 s Y ~ 23 ; GOSUB 1950

2100 PR INI...f'YPE DENOMINATOR; ~"

2110 XA » 24 : GOSUB 2200
2120 D 1 ~ AN

2130 REM CHECK ANSWER
2140 IF N1=N AND D1«D THEN GOSUB 2330
2150 IF N I O N OR D I O D THEN GOSUB 2500
2160 FOR T = 1 TO 2000 ; NEXT T
2170 RETU RN
2180 REM

2.190 REM ACCEPT ANSWER
2200 X - XA
2210 GOSUB 1950
2220 PRINT "
2230 GOSUB 1950
2240 INPUT ANT
2250 REM REJECT NON NUMERICAL.. VALUES
2260 IF A S C ( ANT) < 48 THEN 2200
2270 IF A S C ( ANT) > 57 THEN 2200

22.80 AN = VAl... ( ANT )
2290 RETURN
2300 REM
2310 REM REWARD ROUTINE
2320 REM GREE N SCREEN
2330 POKE 53280, 5 ; POKE 53281, 5
2340 PR I NT " C SHI FT /CLP / HOME II "
2350 REM INCREASE SCORE
2360 S = S + 1
2370 REM INCREASE DI FFICULTY
2380 DF - DF + 1
2390 IF DF > 17 THEN DF = 17

2400 PRINT C H R T ( 5 )

2410 FOR I = 1 TO 11

2420 PRINT "WELL DONE. THAT IS THE " ;

2430 PRINT "CORRECT ANSWER."
2440 PRINT
2450 NEXT I
2460 RETURN
2470 REM
.2480 REM CORRECTION ROUTINE

46

Chapter 2 Small is Beautiful

2490 REM YELLOW SCREEN
2500 POKE 53280, 7 : POKE 53281, 7
2510 PRINT H I! SHI FT/CL P/HOME 3"
2520 REM DECR EASE DIFFICULTY
2530 DF * DF - 1
2540 IF DF < 1 THEN DF = 1
2550 FOR I = 1 TO 11
2560 PRINT " NO. THE CORRECT "5
2570 PRINT "ANSWER IS " N "/" D
2580 PRINT
2590 NEXT I
2600 RETURN

REA D Y .

Commentary

The control module for Fraction lies between 1020-1060, which form a
loop calling up initialisation, selection, drawing and testing routines. The
program does not come to an end unless RUN/STOP is pressed.

Lines 1090-1140 are the initialisation routine. The variables S and G are
set equal to zero at line 1110. They record the score the child has achieved
and the number of fractions attempted. The variable DF is initialised by
line 1130. DF controls how hard each fraction is. The smaller the value of

DF, the smaller the numerator and denominator of the fraction drawn on
the screen. The value of DF is continuously monitored during the execu
tion of the program, so that when the child types in a correct answer the
level of difficulty increases. If an answer typed in is incorrect, the value of

DF is decreased so that the fractions become easier. It is not quite this
simple, as a random factor is introduced as well, but DF does determine the
overall trend towards harder or easier examples.

The fraction is generated between lines 1160-1320. The denominator, D,
is selected at line 1170. DF enters into the expression as the number that the
random fraction RND(l) is multiplied by. Line 1180 relates the size of the
numerator, N, to that of D. Obviously, the way in which the two numbers
are generated ensures that the numerator is smaller than the denominator,
as is necessary.

Lines 1210-1290 relate the value of the variable W to that of D. W is used
in the following routine when the diagram of the fraction is drawn on the
screen. Here, however, it is adjusted to give the largest possible diagram

for the fraction chosen. Finally, this routine calculates a value for the

47

Programming for Education on the Commodore 64

variable LD in terms of W and D. LD allows the subsequent calculation of
the top lefthand corner of each division of the fraction.

Lines 1340-1890 form the routine which places the fractional diagram on
the screen. It is built up quite naturally in a series of blocks or divisions
corresponding in number to the size of the denominator.

After the screen has been cleared by line 1370 and the title and other
headings placed by lines 1380-1440, a lengthy FOR. .. NEXT loop, from
lines 1470-1810, constructs each division of the diagram in turn. At the
beginning of this loop, a new value is first calculated for LD for the current
division. The J loop between lines 1520-1570 draws the top and bottom of
the division in black. A subroutine at lines 1910-1930 is used by this loop,
and also for all successive plotting on the screen. This is followed by a brief
sound effect to help draw attention to the process of building up the dia
gram and hence to aid the child’s counting. The sound is generated by the
various POKEs between lines 1590-1640. After this, the lefthand edge of
the division is plotted by the loop between 1650-1690.

So far, only three sides of the division have been drawn. The enclosed
area is coloured in by the two nested FOR. .. NEXT loops from

1750-1800. The colour the area is plotted in is chosen at lines 1710-1740.
The numerator of the fraction appears in green and the remaining divisions
in yellow. Line 1810 ends the I FO R.. .NEXT loop.

After the D divisions are drawn, there is still the extreme righthand edge
of the diagram to be filled in. The loop between lines 1850-1880 does this.
Note how the same subroutine has been repeatedly called during the whole
of the construction of the diagram.

Lines 1990-2160 make extensive use of the PRINT TAB routine between

1940-1970 to format the presentation of the question on the screen.
Another subroutine at lines 2190-2290 checks that acceptable values are
typed in. Lines 2140 and 2150 then select either reward or correction

routines at the end of the program. It is here that the value of DF is adjusted
to correspond to the degree of success or failure the child is experiencing.
Success will lead fairly quickly to harder examples, whereas constant

failure would lead to the child using the program being shown a diagram of

7 over and over again, together with the correction routine. Although it is

quite simple to arrange for programs to be self-adjusting to the child’s level
of ability, nevertheless such an arrangement allows far more effective
learning programs to be constructed.

48

CHAPTER 3

Words, Words, Words

Handling words on a computer — sorting things — Alphasort: a

program to sort words into alphabetical order — numbers in strings

— Simon: a game to improve memory — diversity o f subjects in

primary schools — problems in spelling — different approaches —

context clues — Hangman: a multi-purpose spelling program —
research skills — Anagram: clues from word order.

So far in the book, the majority of programs have involved some sort of

maths skills. The 64 contains many facilities that make the handling of

words much easier. As has been mentioned before, computers are just as

happy manipulating letters as figures. Numbers are stored as numeric

variables, such as X or COUNT, and strings of characters as string varia

bles, such as A$ or BOOKS. Each character in the 64 has a code number that

refers to it, so 65 stands for A, and 90 stands for Z. You can check this out

yourself by entering this short program.

10 FORN = 65 TO 255
20 PRINT CHR$(N)
30 NEXTN

The function CHR$ converts the Commodore code to its character
equivalent, so you will see the alphabet printed out if you RUN the pro
gram. (This will be in upper case if you are in the normal mode after switch
ing on, or in lower case if you have changed modes by pressing SHIFT and
the Commodore key [C = ] at the same time.)

The function that does the reverse of CHR$ is ASC. ASC is short for
ASCII, the initials of the American Standard Code for Information Inter
change. Although the 64 has its own codes for graphics symbols, it follows
ASCII codes for letters and numbers. This program shows you how ASC
works:

10 PRINT “PRESS A KEY”
20 POKE 198,0
30 GET Z$:IF Z$ = THEN 30

Programming for Education on the Commodore 64

40 C = ASC(Z$)

50 PRINT C
60 GOTO 10

Commentary

Line 20 clears the keyboard buffer (a temporary memory store for key
board input).

Line 30 reads the keyboard and repeats until a key is pressed. Note that
there is nothing between the two quote marks. This is called an empty
string.

Line 40 assigns the ASCII code of the key pressed to the variable C.

Lines 50 and 60 print the code and send the program back to the start.

If you run this program, you will discover many useful things. Apart from
pressing letter keys, try pressing number keys, the arrowed cursor keys,
and the function keys. You will find that all the keys generate codes except

[RESTORE], [CTRL], [SHIFT] and [SHIFT LOCK], [C = ] and

[RUN/STOP] on their own. Many keys, such as A, have three codes,
depending on whether you are pressing [SHIFT] or [C = ] at the same time.

The key A normally has a code of 65, but it produces 193 with [SHIFT]
and 176 if [C = ] is also held down. This is useful in programs, as you can
check which keys are being pressed at any time.

If you have a program that requires a word or phrase to be input into a

string, the length of the string can be checked by using the function LEN. If

you enter directly

X$ = “ HELLO”

then

PRINT LEN(X$)

the result 5 will appear, as HELLO has five characters.

Other string functions are RIGHTS, LEFTS, and MIDS. RIGHTS

returns the righthand portion of a string, LEFTS the lefthand portion, and

MIDS can extract a portion from anywhere in the middle. To see how they
operate, try this:

10 AS = “ ABCDEFGHIJ”
20 PRINT RIGHT$(A$,4)

50

Chapter 3 Words, Words, Words

30 PRINT LEFT$(A$,4)
40 PRINT MID$(A$,2,6)

If you RUN this, it will print GHIJ in line 20, as these letters are the last
four letters on the right of the string. ABCD will be printed out in line 30, as
they are the first four letters on the left of the string. Line 40 will print out
BCDEFG, as these are the six letters starting from the second character in
the string.

This program will show you how the 64 can search through strings using
these functions:

10 PRINT “ENTER A WORD”
20 INPUT A$
30 IF LEN(A$)< 3 THEN PRINT “ TOO SHORT” :GOTO 10
40 PRINT A$“ IS ” LEN(A$)“ CHARACTERS LONG”
50 PRINT “ IT STARTS WITH ”LEFT$(A$,1)
60 PRINT “ AND ENDS WITH ” RIGHT$(A$,1)
70 PRINT “AND CONTAINS ”MID$(A$,2,LEN(A$)-2);
80 PRINT “ IN THE MIDDLE”

Because the 64 gives all the keyboard characters numbers, it is possible to
sort words into alphabetical order according to their ASCII codes. This
program prints out a list of the words in the order in which they were input,
then sorts them and prints them in their new order. Although 20 words can
be sorted in about four seconds, 100 take about a minute and a half, as the
number of individual comparisons grows. Enter line 245 S = S + 1, and

PRINT S at the end, if you want to see how many comparisons were made
between words.

Alphasort

100 REM *** ALPHASORT ***
110 REM
120 REM *** AJS 5/8/83 •***
130 REM
140 REM
150 INPUT "NUMBER OF WORDS";N
160 DIM A*<N+1>
170 FOR X = 0 TO N ~ 1
180 INPUT A*(X>
190 NEXT X

51

Programming for Education on the Commodore 64

EOR X

20 0
21 0 PRINT At (X )
22 0 NEXT X

FOR K = 0 TO N -1

230
240

FOR L

250

IF A#

= 0 TO

= K+l

(L) >=

N — 1

TO N

At <K)
260 Ut = At (L)
270 At <L) = At (K
280

At (K) = Lit

)

290 NEXT L

300 NEXT

FOR X = 0 TO N

310

K

320 PR INI- At (X )

330 NEXT

R E A D Y .

Commentary

There are one or two new ideas in this program. A sorting routine needs to
hold the words, not in one variable, but in an array. This has to be DIMen-
sioned so that some space in memory is reserved for the words that will be
stored in it.

Line 160 reserves space according to the number of words to be sorted.

Lines 160 to 220 print out the words to be sorted.

Lines 230 to 300 contain the sorting routine. There are two loops, K and L,
and the ASCII codes of the words are compared in line 250. If a word has a

higher code than the one after it, they are swopped in the list. The loop

compares all the words against each other until they are in alphabetical
order.

Lines 310 to 330 print out the new list.

Strings and things

As has been mentioned previously, string variables can contain any key
board character, not just letters. Although you can redefine characters to
be any shape you like and use them in your programs, all Commodore
computers contain graphics characters that can be produced by the key
board. Your 64 contains two character sets, but only one can be used at any
one time. When it is switched on, the 64 is in upper case mode. As you press
keys, upper case characters are produced. Pressing the [SHIFT] key and a
letter key gives you the graphic character printed to the right on the front of

52

Chapter 3 Words, Words, Words

the key. Pressing the [C = ] key and a letter key gives you the graphic char
acter printed to the left on the front of the key.

If you hold down the [SHIFT] and [C = ] keys at the same time, you can
switch between upper and lower case modes. Lower case mode is a little like
using a typewriter: pressing a letter key gives you the lower case version,
and pressing [SHIFT] with the letter gives the upper case version of that
letter. Pressing the [C = ] key and a letter key still gives you the graphic
character printed to the left on the front of the key.

You can switch to upper case mode in a program by including PRINT
CHR$(142) in a line. To switch to lower case mode, use PRINT CHR$(14).

The graphics characters can be used to draw pictures on the screen, by
using quotes to surround the graphics, just as if you were printing words.

Numbers in strings

You have probably seen that there are two ways to print 123 on the screen.
You can enter

PRINT 123

or

PRINT “ 123”

Although you see the same figures appearing on the screen, it is important
to realise the difference that the 64 sees. 123 is seen as a number, with the
value 123. “ 123” is seen merely as a string of characters. To see the differ
ence, try this as a direct command:

PRINT 123 + 123

You should get 246 as the answer, because the computer understands these
to be numbers. If you enter:

PRINT “ 123” + “ 123”

you will get 123123, because the 64 treats them as strings.

Although they are completely different, numbers can be turned into
strings and vice versa. To turn 123 into a string, you can use the STR$
function, eg

A$ = STR$(123)

53

Programming for Education on the Commodore 64

The reverse of this is achieved by using the VAL function. Even though
strings can’t normally be considered to be numbers, they do have a value.

PRINT VAL(“ 123”) + 1

will print 124. If the first character in the string is not a -I- or a - or a
figure, the value is zero.

Simon

In this program, the fact that strings can be concatenated (added together),
is used as the basis for a memory game. A string contains the STR$ version
of numbers chosen at random from one to eight, and the object is to
remember their order. The length of the string increases by one each time a
correct answer is entered.

The game of Simon is usually played with colours and sounds as extra
memory aids. The 64 stores the code of the colour in which text is printed at
location 646 in the memory. If this is POKEd with numbers from 0 to 15,
the sixteen available colours can be selected.

The number keys on the 64 have colours printed on them, BLK, WHT,
etc. The numbers on the keys are one higher than the code to be POKEd to
646, hence the line that subtracts one from the value of the string.

The sound commands are a little more complicated. They are explained
in more detail in the program notes.

10 REM ***

SIMON •***

20 REM
30 REM ***

AJS 5/6/83 *•**
40 REM
50 REM

60 REM ***

INSTRU CT IONS ***
70 REM
80 PRINT C H R * (147):P 0 K E 5 3 2 8 1,0
90 PRINT

100 PRINT" THIS IS A GAME OF MEMORY"
110 PRINT

120 PRINT" YOU WILL BE SHOWN A SERIES"
130 PRINT
140 PRINT" OF FIGURES. THESE FIGURES"
150 PRINT
160 PRINT" WILL SOON DISAPPEAR AND YOU"

54

Chapter 3 Words, Words, Words

.170

PRINT

180

PRINT" MUST TYPE THEM IN, IN THE"

190

PRINT

200

PRINT" RIGHT ORDER. THE NUMBE R OF"
PRINT

210

220

PRINT" FIGURES WILL INCREASE BY ONE"

230

PRINT

240

PRINT" EACH TIME."

250

PRINT

260

PRINT" PRESS SPACE BAR TO GO"

270

GET Z*:IF Z$="" THEN 270

280

PRIN T C H R*(147):P 0KE53281,12

290

REM

300

REM *** MAIN GAME LOOP ***

310

REM

320

FOR Z= 1 TO 10

X-INT(RND(0)*8)+1

330
340

X*=S T R * (X ):X $ = MID* < X * ,2,1)

Y4---YT+XT

350
360

60SUB 490: P O KE 198,0
370
380
390
400
410
420
430
440
450
460
470
480
490
500

INPUT"ENTER YOUR G U E S S " ;G*
IF G$ = Y* THEN S=S+1

IF G* < >Y* THEN Z = 11:GOSUB630
NEXT Z
REM
REM *** SCORE ROUTINE ***
REM
PRIN T"YOU SCORED" S
PRINT" PRESS ANY KEY TO GO AGAIN"
GET Z*:IF Z#=""THEN 460
RUN
REM
REM *** COLOU R PRINT SUBROUTI NE ***
REM

510 PRINT
520 FOR N = 1 TO LEN(Y$>

530 A$= M I D$(Y$ , N ,1):V = VAL<A*)
540 POKE 646,V-Is REM CO LOUR VA LU E
550 PRINT A*;" ";
560 GOSUB 700
570 NEXT N
580 PRINT
590 FOR F'AUSE= 1 TO 1000: NEXT PAUSE
600 P R I NTC H R * (147):P0KE 6 4 6 ,1

55

Programming for Education on the Commodore 64

610 RETURN

62.0 REN
630 REN •*** FAULT SUBROUTI NE ■***
640 REN
650 PR I N T"NISTAKE!! IT WAS "Y$
660 RETURN
700 REN
710 REN *** SOUND SUBROUT INE ***
720 REN
730 SC ■ 54272
740 POKE SC-i-24,15: REN VOLUME
750 POKE S C +4,33
760 POKE SG+5,10s POKE SC+6,4
770 V=V*2 000
780 HIGH = INT(V/256)SLOW = V-HIGH*2 56
790 POKE S C + 1,HIGH sPOKE S C ,LOW
800 FOR PAUSE = 1 TO 400s NEXT PAUSE
810 PO KESC +4,0
820 R ETURN

REA D Y -

Commentary

Line 80 shows another way of clearing the screen — PRINT CHR$(147).
The second statement sets the background colour to black.

Lines 100 to 260 contain the instructions.

Line 270 waits until any key is pressed. Line 280 clears the screen and sets
the background colour to grey.

Lines 320 to 400 form the loop which provides 10 figures.

Line 330 chooses a number at random between 1 and 8. Line 340 turns the
number into a string, and the second statement strips away the first char
acter, a space. Line 350 adds the new figure to the existing string.

Line 360 sends program control to the print routine and clears the key
board buffer to prevent cheating!

Line 380 checks the input against the string and increments the score by
one. Line 390 ends the Z loop if the answer is incorrect, and sends the
program to the fault subroutine.

56

Chapter 3 Words, Words, Words

Lines 440 to 470 print the score and start the program running again.

Lines 520 to 570 print the separate figures in the string after their colour
codes have been POKEd into memory location 646. Line 550 prints a space
between each figure.

Lines 590 and 600 provide a delay of about two seconds before the string
disappears.

Line 650 contains the fault subroutine.

Line 730 sets SC equal to the starting address of the 6581 SID sound chip.

This makes all the subsequent addressing of locations in this chip easier to

follow.

Line 740 sets the volume to maximum. Line 750 sets the total quality of

voice 1 to a sawtooth waveform. Line 760 sets the envelope of voice 1

(attack/decay and sustain/release).

Line 770 sets the frequency of the note by multiplying the value of the
figure in the string (V), by 2000. The SID chip is capable of producing notes
of a frequency that can be stored in two bytes. The highest value that could
be stored is therefore 256*256 or 65536. Line 780 calculates what should be
POKEd into this two-byte frequency store to produce the required note.

Line 800 controls the length of the notes. Line 810 sets the waveform con
trol register to zero.

Diversity of subject areas

There are many areas of English teaching in which the computer can prove
a useful aid. Because of its fast sorting ability and accurate input check, it
can be used to help in spelling, alphabetical ordering, punctuation and
grammar in general.

It seems a little unfair to divide up the chapters in this book into the
traditional subject categories of maths, English, geography, etc, as most
teachers in primary schools would agree that such divisions are hard to
make. A day spent in looking at a local shopping centre, for instance,
might cover such areas as maths — surveys of people entering each shop;
geography — the countries that provide the goods; history — how the area
has changed over the years; art — drawing the shops; English — writing
about the area, etc.

Such a topic-based approach is closer to the child’s experience of the

world, and subject divisions would be artificial. Certain basic skills still

57

Programming for Education on the Commodore 64

need to be taught, however, and this book would lack any structure if the
programs were not divided up in some manner.

It is with this in mind that the programs in this chapter have been

included. They attempt to help the teacher or parent instil basic spelling
and comprehension skills.

Hangman

Some children are lucky and have no difficulty in spelling. Others attempt
a phonetic approximation, and yet others never seem to grasp the idea.
Although poor spelling often goes hand-in-hand with poor reading skills,
there are many good readers who reach adulthood and still suffer from
difficulties with their spelling. Traditional methods of learning words by
heart for a weekly test are no bad thing if the words are relevant to the
child’s immediate situation, eg if they come from a project or topic that is
being studied. If the child uses the words in their proper context, the spell
ing is reinforced.

There are two approaches here — one is to show the context of the word

and to offer a multiple choice of possible spellings. The other approach is
to build up the word slowly, with spaces for missing letters. The game of
hangman is an ideal vehicle for this approach. The program that follows

builds up a picture of lependu, as in the traditional game, and 10 guesses
are allowed before the victim is finally throttled.

Words to be selected are held in DATA lines, so there is no problem in

changing these to words relevant to a topic, or to those displaying a parti
cular spelling point, such as ‘ie’ and ‘ei’ words. You could even use the
program to help learn foreign words. The only requirement is that the total

number of words should not change, as the READ statement needs 20
words. If you want a larger selection, then the number may be altered as
detailed in the program notes.

1000 RE M ** * HA N GM AN ***

1010 REM

1020 RE M ** * A JS 2/ 8/8 3 ***

1030 REM

1040 P0K E5 3281, 1s P0KE6 46 ,0
1050 GOSUB6000:REM*** INITIALISATION ***
1060 GOBU B7 000 :REM*** INSTRUCTIONS ***
1070 GOSU B2000:REM*** GAME ***
1080 GOTO 1070

200 0 R EM *** GA ME S U BR O UT INE ***
200 5 REM

58

Chapter 3 Words, Words, Words

201 0 R E ST OR E
202 0 F OR N= 1TO I N T ( R N D<0 )* 20 ) + 1
203 0 R EA D W$
204 0 N EX T
206 0 P RIN T""
207 0 X ~ 5: Y = 15 : 6OS U B40 0 0
208 0 F O RN =l TO LE N< W$ )
2090 P RIN T"- ";
210 0 N EX T N
212 0 S C =0 :Z= 0
213 0 X=5: Y=20s GO S UB 4 00 0
214 0 G $ = " ":P R INT " YOU R GUESS";

214 5 P O K E 1 98,0
215 0 IN PU TG*: FL AG =1
215 5 IF G$= W$ TH EN G OS U B 30 0 0 :RE T U RN
216 0 L N = L E N < W$)
217 0 IF L E N (G $ )< >LN A ND LE N< 6* >> 1 TH EN X=1 5sY=20s

GO SUB 4 00 0

218 0 IF L E N ( G $ ) O L N A ND LEN <G $ ) > 1 T HE N PRIN T"

219 0 IF LE N < G # ) < >LN AN D LJEN<G$>>1 TH EN GO TO 2130
220 0 IF L EN< G * ) = 1 THEN X=Z : Y= 2 3: G OSU B 40 0 0

2 2 1 0 IF L.EN <G* )=1 THENPRI NTG *

222 0 Z = Z-M.
223 0 F OR N = 1 TO LN
224 0 IF G $= M ID * ( W$ , N ,1 ) TH E N G O SU B 2 50 0
224 5 IF6 f=MIDt- (W# , N , 1) T HE N F LAG =0
225 0 N EX T N

226 0 IF FL AG < >0 T HE N SC=SC,+1: GOS U B2 6 00

227 0 X =24:Y=0s GO SU B40 00

228 0 I F S O 0 T H E N P R INT " LIV ES LEF T - >" 1 0- S C

229 0 IF SC C10 THE N G OT O 213 0

230 0 Y~24s GOS U B4 000

230 5 R EM •*** WOR D N OT G UE SS ED ***

231 0 FOR N = 1 TO 1 0sPR I N T " H E L P !! !! "s PR I NT :N EXT
232 0 PR INT "T H E WO RD WA S "W*
233 0 P R IN T
233 5 P O K E 198,0
234 0 P R IN T " PR E S S THE SPACE BAR TO GO"
2350 GET Z$:IF Zt="" TH EN 23 50
2360 RE TU RN
237 0 R EM

250 0 R EM *** PRI N TIN G COR RE CT L E TTE RS ***
250 5 REM
251 0 X =4+ N :Y= 1 5s G O SU B 400 0
252 0 P RIN TG $
259 0 RE TU RN
259 5 R EM
260 0 REM ** * H AN G ING S U BR O UT I NE ** *

it

59

Programming for Education on the Commodore 64

605. REM

£>10 P0KE646 , (S C ) ANDSC >2: REM COLOURPRINT
£>20 X=38: REM *** UPRIGHT ***

630 IFSC=1 T HE N F O R Y - 19T03 S T E P-1sG OSUB 4000:

PR I NT C HR * (166) -.NEXT

640 Y=2: REJM *** CRO S SP I EC E ***
650 I FSC=2 T HE N F 0R X= 29T03 8: GOSUB4000-. PR IN T CH RS

(166) -.NEXT

660 X «29:REM ** * ROP E ***
670 IF SC=3 T HE N F 0 R Y= 3 T 05 : GOS U B 40 0 0 :PR I N TCH R *

(180) -.NEXT
720 X=27: Y=5-.GOSUB4000-.REM F AC E *
730 IF S C =4 T HE N P R I N T C H R * (100 )C H R * (101);
740 IF SC=4 T HE N P R I N T C H R * (102)C H R * (103)
745 X=27s Y=6 s GO S UB4 00 0
750 IF SC=4 T HE N P R I N T C H R $ (104)C H R $ (104);
760 IF SC= 4 T HE N P R I N T C H R S (106)C H R S (107)
765 X =27 s Y = 7 : GOSLIB4000
770 IF SC=4 TH EN PRINTCHR-fc(1 08)C H R $ (109);
780 IF S C=4 T HEN P R I N T C H R * (110 )CHR$(111 )
785 X = 2 7 :Y=8s GOS U B4 0 0 0
790 IF S C=4 T HE N PR I NTC HR* (112) CHR * (113);

ro ro ro ro ro ro ro ro ro ro ro ro ro ro ro w ro ro w

10

800 IF S C=4 T HE N P R I N T C H R $ (114 )C H R $ (115)

10

815 X= 28 :R EM ** * B ODY ***
820 I F S C = 5 TH E N F 0R Y = 9T0 13 s GO SU B 40 0 0 s PRIN TCH R*

(166) C H R $ ( 16 6) sNEXT
825 X=s28s REM ** * L .A RM ***
830 IFSC = 6 THEN F 0 R Y = 9 T 013: X = X - 1:GO SUB 400 0:

PR I NT C H R* ( 1 69 > sN E X T
835 X=29s RE M *** R.AR M ***
840 IF SC= 7 T HE N F 0RY =9 T013: X = X + 1: GOSUB4000-.

PR I N TC HR $ (127) -.NEXT
845 X= 29 :R EM ** * L .L EG ***

850 IFSC=8 THEN F0R Y= 14 T0 18:X=X-1:GOSUB4000:

PR INTC H R $(169):NEXT

855 X=28s REM *** R .LEG ***

860 I FSC=9 T HE N F0R Y= 14T01 8: X = X+1 -. GOSU B40 00:

ro ro to ro ro ro ro ro ro

PR I N TC H R$( 1 27 ) i NE X T

298 0 P 0 K E 6 4 6 ,11
2990 R ETU RN
300 0 RE M
301 0 R EM *** SUC CE S S R O UT IN E ***
302 0 REM
3030 X =5:Y= 15s GOS U B4 000
304 0 P RI NTW *
3050 FOR PA US E = 1 TO 2000; NEX T PA US E
306 0 X = 0 : Y = 11 s GO S UB 4 00 0
307 0 P R IN T"T H AN K S FO R S AVING ME!"

60

Chapter3 .Words, Words, Words

308 0 P RI NT
309 0 PR I NT" YOU G UE S SE D "W$
31 00 PR IN T

3105 P O K E 198, 0
311 0 PR I NT " P RE S S SPA CE BAR TO GO"
312 0 GET Z$:I F Z $ = " " THEN 31 20
313 0 RE TU R N
400 0 R EM
401 0 REM *** 'PRINT AT' R OU T IN E ***
402 0 REM
4030 P 0 K E 7 8 2 ,X s P 0 K E 7 8 1,Y s SY S6 55 2 0 s RETU RN
600 0 REM
6010 REM ** * M OV E CH A RA C TER S ET * **
60 20 REM

603 0 P R I N T C H R $ (142)

6040 PO K E 5 2 ,48 : P 0 K E 5 6 ,48

605 0 P 0 K E 5 6 3 3 4 ,P E E K (56 33 4) AN D2 54

60 60 P O K E 1,P E E K (1)A N D 2 5 1

6070 F O R N = 0 T O 1023

60 80 P O K E 12 2 8 8 + N ,P E E K (53 2 4 8 + N )

60 90 NEXT N

6100 P O K E 1,P E E K (1)0R4

611 0 P 0 K E 5 6 3 3 4 ,P E E K (5 63 34) O R 1

612 0 P 0 K E 5 3 2 7 2 ,(P E E K (5 327 2)A N D 2 4 0 )+12

613 0 REM

6140 FO R N=1 T O2 0 : R EA D Z $: N E X T

6150 FOR N =0 T O1 2 7

61 60 READ Z

6170 P O K E 12 2 8 8 + 6 8 * 8 + N ,Z

61 80 NE XT N

6190 RE TU R N

7000 REM
7010 R EM *** I NS TR UCT IO NS ** *

70 20 REM

7030 PRINT ""
7050 PRI NT"
706 0 P RI NT
707 0 PRINT"
708 0 P RI NT
709 0 P RIN T"
7100 PR IN T
7110 PRI NT"
7120 PR IN T
713 0 P RINT"
714 0 P RI NT
71 50 PRI NT"
716 0 P R IN T
717 0 P RIN T" WRONG, PA RT OF THE M AN APP EA RS "
718 0 P RI NT

IN TH IS GAME, YO U W IL L BE"

GI VE N A ROW OF D AS HE S"

EA CH DAS H S T AN DS F OR A LET TE R"

YOU H AV E TO GU E SS THE L ET TE RS "

IF YO U A RE RI GH T TH E LETT ER "

WILL APP EAR. IF YO U ARE "

61

Programming for Education on the Commodore 64

719 0

720 0

721 0

722 0

723 0

724 0

725 0

726 0

727 0

728 0

729 0

900 0

901 0

902 0

903 0

9040

905 0

906 0

907 0
908 0
909 0
910 0
911 0
912 0
913 0
914 0
915 0
916 0
917 0
918 0
919 0
920 0
921 0
922 0
923 0
924 0
925 0
9260

PRI NT" AND YO U LOSE A LIFE. IF YOU"
PRINT
PRI NT" T HI NK Y OU KN OW TH E W OR D YOU"
PRINT
PRIN T" MU ST SP EL L IT CO R REC T LY TO"
PRINT
PRINT" SAV E THE PO OR MAN!! "
PRI NT
PRINT" PRE SS T HE SP AC E BA R TO GO"
GET Z$:IF Z $ = " " THE N 728 0
RE TU R N
REM *** DAT A F OR WO RD S ***
REM
DA TA M O N DA Y , TUE S D AY, W EDN E S DAY
DAT A T H U RS D A Y, F R I DA Y , SAT U R DAY
DA TA SUN D AY , J AN U A RY, F E BR U A R Y
DAT A M A RC H , A PR I L , MA Y , JUN E , JUL Y
DA TA AU G UST , S EPT E M BER , O CT O B E R
DAT A N O VE M B E R, D E C EM B E R,Y E A R
REM
REM *** DAT A F OR FA CE ***
REM
DA TA 0 , 0 ,0 , 0,3 , 3 ,15 , 15
DAT A 15 , 1 5, 6 3 ,6 3 , 25 5 ,2 5 5 ,2 5 5 ,2 5 5
DA TA 2 40 , 2 4 0, 2 5 2 ,2 5 2 ,25 5 , 255 , 2 55, 2 5 5
DAT A 0 , 0, 0 , 0 ,1 9 2 , 19 2 , 240 , 2 40
DAT A 63 , 63, 6 3,6 3 , 60, 6 0 ,6 3 , 6 3
DAT A 25 5 ,25 5 , 63 , 6 3 ,1 5 , 1 5, 6 0 , 60

DATA 2 5 5 , 255 , 2 52, 2 5 2, 2 4 0 ,2 4 0 , 60 , 6 0

DA TA 25 2 , 252 , 2 52, 2 5 2, 6 0 , 60 , 2 5 2, 2 5 2

DATA 6 3 , 63 , 6 3, 6 3 , 60 , 6 0 ,1 5 , 1 5
DA TA 25 2 ,25 2 , 240 , 2 40, 4 8 ,4 8 , 6 3, 6 3
DAT A 63 , 63 , 1 5 ,1 5 , 1 2, 1 2 , 25 2 , 252
DA TA 2 5 2 ,2 5 2 , 25 2 , 252 , 6 0,6 0 , 24 0 , 2 40
DA TA 3 , 3 ,0 , 0 ,0, 0 ,0 , 0
DAT A 20 7 , 20 7 , 2 40 , 2 4 0, 6 3 ,6 3 , 1 5, 1 5
DA TA 2 43 , 2 4 3, 1 5 ,15 , 2 52, 2 5 2, 2 4 0 ,2 4 0
DA TA 1 9 2,1 92, 0,0 ,0, 0, 0 ,0

READY.

Commentary

As this is a fairly complicated program, we have inserted a lot of REMs to
inform you of what is happening.

Lines 1040-1070 constitute the control module. Line 2000 begins the game

subroutine.

62

Chapter 3 Words, Words, Words

Lines 2020-2040 choose a word, W$, at random from data. Line 2070 sets
the ‘print at’ coordinates. Lines 2080-2100 print dashes according to the

number of letters in the word. Line 2145 empties the keyboard buffer.

Line 2150 accepts the guess, G$, and sets the variable FLAG to a one. This
is only changed to a zero if a correct letter is input, and is used in line 2260 to
check if part of the gallows should be drawn.

Line 2155 checks to see if the whole word has been entered. If it has, the
program jumps to the winning routine.

Line 2160 sets variable LN to the length of the chosen word, W$.

Lines 2170-2210 check the length of the guessed word against the chosen
word. If more than one letter is input, it is ignored, unless it has the same

number of letters as W$.

Line 2220 contains the counter for the number of incorrect guesses, Z.

Lines 2230-2250 check each letter of W$ to see if it contains the guessed
letter, G$. If any letter is the same, subroutine 2500 prints it in the correct
place. The flag is also changed to prevent part of the gallows being built.

Line 2270 and 2280 print the number of lives remaining at the top of the
screen.

Line 2290 sends the program back to the start of the guess loop if less than

10 incorrect guesses have been made. On loop 10, the program continues.

Line 2500 is a short routine to print a letter in the correct place. It uses the
loop counter N, to tell it where to put the letter.

Lines 2600-2990 contain the rather large drawing routine to construct the
gallows and the man.

Line 2610 uses the number of incorrect guesses, SC, to control the printing
colour.

Lines 2620 and 2630 use a loop to draw the upright post. CHR$(166) is a
graphics character like a tiny chessboard.

Lines 2640 and 2650 use another loop to draw the crosspiece. GOSUB
4000, to the ‘print at’ routine, ensures that the next print position is con
trolled by the X value in the loop counter.

63

Programming for Education on the Commodore 64

Lines 2730-2800 draw the head. This is made up from defined characters

held in DATA statements. The ‘print at’ routine is again used to control the

position of the head.

Lines 2815-2860 use the same principle to draw the rest of the body

according to the value of the variable SC.

Line 2980 POKEs the printing colour back to grey. The success routine also
uses the ‘print at’ routine to print the correct word and a thank-you
message.

Line 4030 contains the short ‘print at’ routine where the new X and Y
coordinates are POKEd into memory. Without this routine, the effects in a
program like this would have been much more difficult to achieve.

Line 6000 starts the character-moving routine. Characters cannot be rede

fined on the 64 unless the character ROM is copied into RAM.

This is exactly the same structure as that in the program BigL, so refer to

those notes for more detail.

Lines 6140-6180 redefine the 16 characters from number 68 onwards.
Note that this number is not the same as the ASCII code and, when the
characters are printed, 32 must be added to the number of the character
before it can be used after a CHR$.

Lines 7000-7290 contain the instructions.

Lines 9000 onwards contain all the data for the program. It is divided into
two sections, the first containing the words to be used, and the second the
data for the redefined graphics used to draw the face.

Anagram

It is hoped that the programs that are included in this book reflect to some
degree the belief that children do not come to school simply to acquire
knowledge that may or may not be useful in the future. Children need to
learn many skills at primary age, and, apart from the most important
(social skills), thinking skills and the ability to research and store informa

tion must rank high in the list.

Although spelling is important in its own right, the child who has diffi
culty with spelling will be at a disadvantage when it comes to finding
information from reference books. There is little point in giving a child an

64

Chapter 3 Words, Words, Words

encyclopedia and saying ‘Find out all you can about beer production in
Belgium’ if the child cannot spell Belgium and does not know how to find
the information in the first place. Information from a book may not be as
good as firsthand experience (especially in the example in question!), but it
is better than no experience at all.

The following program can be used as a spelling aid, or in any other

subject area to familiarise children with new words. Anagram allows the
parent or teacher to load data lines with a fresh vocabulary. The child is
presented with a scrambled version of the word on the screen and has to
input the word, spelt correctly. Points are gained for getting the word
right. The final score is shown after 10 words have been displayed.

100 REM
1010 REM *** AN A GR A M G AME ***
1020 REM
1030 RE M *** AJS 4 /1 0/ 8 3 ***
1040 R EM
1050 GO SU B 1500 s REM IN STR
1060 FOR TRY = 1 TO 10
1070 GO SUB 2 00 0 s REM GET WO RD
1080 GO SU B 3000s REM M IX W OR D
1090 GO SUB 400 0 s REM GAME
1100 NEX T TRY
1110 GO SU B 5 0 0 0 sREM S CO RE
1120 STO P
1499 REM
1500 REM *** I NS TRU CT IO NS ***
1510 REM
1520
1530
1540
1550
1560
1570
1580
1590
1600
1610
1620
1630
1640
1650
1660
1670
1680
1690
1700

P0K E53 28 1, 1s PO KE 6 46 ,0
PRI NT CH R$ <1 47 >
PRI NT
PRINT" YOU WILL BE SH OW N A NU MB ER"
PRINT
PRINT" OF J UM B LE D UP WORDS"
PRINT
PRIN T" YO U CAN ASK F OR TH EM TO BE"
PRINT
PRIN T" MI XE D UP A GA IN OR Y OU CAN"
PRINT
PRIN T" GUE SS WHA T YOU TH IN K THE"
PRI NT
PRIN T" WORD REALLY IS"
PRI NT
PRIN T" AF TE R TEN WO RD S Y OU W ILL"
PRI NT
PRIN T" BE S HO WN YO UR SCO RE"
PRINT

65

Programming for Education on the Commodore 64

1710
1720
1730
1990

2000

2010

2020

203 0
204 0
205 0
206 0
299 0

300 0
300 5
301 0

302 0

303 0

304 0

3050
306 0
307 0
308 0
309 0
399 0
400 0
401 0
40 20
403 0

404 0

405 0

406 0
407 0
4080
409 0
410 0
411 0
412 0
413 0
414 0
415 0
415 5
416 0
417 0
419 0
420 0
450 0
451 0
452 0

P R I N T ” PR ES S THE S PAC E BA R TD SO"
GET Z*: IF Z*="" TH EN 1720
RE TU R N
REM
REM *** GET WOR D ***
REM
REST OR E

FOR N = 1 TO I N T (RND < 0)*21)+1
READ WD*

NEX T
RE TU RN
REM

REM *** MIX WO RD ***
REM

DU MM Y *= WD*
N W * = " ”
FOR N = 1 TO L EN (D UMM Y*)
IFw R N D (0 )>= .5 TH E N N W * = N W * + M I D * (D U M M Y * , N , 1)

GO T O3 0 60

NW *=M ID * < D U M M Y * , N , 1)+N W*
NEXT N
DU MM Y* = NW *

IF NW * =W D * THE N 302 0
RE TU R N
REM
RE M ** * DISP LAY ** *
REM
P R I N T C H R * (147)
PRINT
PR INT " YO U R JU M BL E D L E TT E RS AR E:- "
PRINT
PRINT N W*

X 1= P E E K ( 782 ):Y 1= P E E K (781)

X= 5:Y = 22 : GOS U B60 00
P O K E 198,0
P R I N T " M .TO MIX, G TO GUESS ?"
GET Z*

IF Z*< >"M" AND Z*< >"G " T HE N 411 0

X = X 1:Y = Y 1:GO SU B 60 00

IF Z*="M" TH EN GO S UB 30 00
IF Z*="M" THEN GOT O 4020

X= 5:Y =2 2 s GO S U B6 0 00

INPU T" EN TE R YO UR GU ES S
IFG* = WD* T HEN G OS U B4 5 00
IFG* O W D * T HE N G OSU B46 00

RE TU RN
REM

REM *** SUC CES S R O UT INE ***
REM

---

>" 5G*

66

Chapters Words, Words, Words

453 0 P RI NT “Y E S ”: SC = SC+1
454 0 P0K.E53281 ,5
45 50 F OR PA US E = 1 TO 2000s NEX T PA USE
45 60 P 0 K E 532 8 1,1
45 70 R E TU RN
460 0 RE M
46 10 R EM *** MI S TA K E R OU T IN E ***
46 20 R EM
46 30 P RI NT 11 NO, “WD*
4640 P 0 K E 5 3 2 8 1 ,2
465 0 F OR P AUS E * 1 TO 2000a NEXT P AU SE
4660 P 0 K E532 8 1,1

4670 R ETU RN

50 00 R EM

50 10 RE M ** * S CO RE R OUT IN E ***
50 20 REM
50 30 P R I N T C H R $ (147)
504 0 PRIN T

50 50 P R I N T “YO UR S CO RE WA S “S C “WO RD S R I G H T ”
50 60 IF SC = 10 T HE N P R IN T “WEL L DONE"
50 70 IF S C >6 A ND SC <10 TH EN PR IN T “F A I R ”
50 80 IF S C< 7 TH EN PR IN T “LE AR N TH EM !!"
50 90
59 90
600 0
601 0
602 0
8990
900 0
901 0
902 0
903 0
904 0
905 0
906 0
907 0
908 0
909 0
9100
911 0

912 0

RE TU R N
REM
REM *** 'PRINT AT' ROU TIN E ***
REM
PO K E 7 8 2 , X s PO K E 7 8 1, Y s SY S 65 5 2 0 s RE TU R N
REM
REM *** DAT A ST A TE M E NT S ***
REM
REM *** E NT ER Y OU R OWN WO RDS ***
REM
REM *** BU T M AK E SU RE TH ER E ***
REM
REM *** ARE TW EN TY ***
REM
DATA A A R D V A R K ,B A B O O N ,CAME L *DON KE Y
DA TA E L E P H A N T ,F L A M I N G O ,GO O S E ,HO RSE
DATA I B E X ,J AC K A L, K A N GA R O O,L E M UR
DATA M O N K E Y ,N E W T „OS T R I C H ,QUA IL
DATA R A B B I T ,S T O R K ,TI G E R ,Z EBR A

READY.

Commentary

Lines 1050-1120 form the control module. Lines 1060-1100 contain the
main loop which selects ten words to guess.

67

Programming for Education on the Commodore 64

Lines 1500-1730 contain the instructions. Line 1520 sets the background
colour to white, and the printing colour to black. Line 1530 clears the
screen. Line 1720 waits for a key to be pressed before the program
continues.

Lines 2000-2060 get words at random from the DATA lines. If you have
more than twenty words in DATA, you will have to increase the size of the
loop in line 2030. RESTORE in line 2020 sets the data pointer back to the
beginning of the list of words each time.

Lines 3000-3090 mix the letters of the word. The loop in lines 3030-3060
goes through the letters of the chosen word one at a time. It builds a new
word by attaching a letter at random to either the front or back of the new
word.

Line 3070 uses DUMMY$ to hold a copy of the new word. Line 3080

checks to ensure that the new word is not the same as the original!

Lines 4000-4200 control the display of the game. Line 4020 clears the
screen. Lines 4040-4060 print the jumbled word.

Line 4070 saves the print coordinates in variables XI and Y1. Line 4080
resets the print position to the bottom of the screen by jumping to the ‘print
at’ subroutine. Line 4090 clears the keyboard buffer.

Lines 4100-4120 allow the input of either M or G. If M is pressed, the
program jumps back to the mix subroutine. If G is pressed, the program
continues.

Line 4155 sends the print coordinates for the bottom of the screen to the
‘print at’ subroutine. Lines 4160-4190 check the guess against the actual
word and send control to the particular subroutine.

Lines 4500-4570 contain the success routine, which simply increases the
score by one and temporarily makes the background green in line 4540.

Lines 4600-4670 contain the mistake routine. This turns the background
colour to red.

Lines 5000-5090 clear the screen and print the score.

Line 6020 is the ‘print at’ subroutine, which sends the coordinates of the
next print position to the operating system kernal.

Lines 9000-9120 contain all the words used. Any twenty words can be

used here, but avoid those with more than 10 letters, as they will extend on

to the next line.

68

CHAPTER 4

Making Friends with your Keyboard

Tackling entry errors — menus — making problems foolproof —
moving the character set — BigL: writing large on the screen — Key
board: learning the keys — Masking: changing binary numbers.

A computer can receive information from a variety of sources. These
include cassettes, disks, joysticks, light pens, even the telephone line and,
of course, the keyboard. In a program, the most common methods of
entering data are via INPUT and GET statements.

You have already seen INPUT used on several occasions. Program exe
cution halts until some information is entered by pressing the [RETURN]
key. GET does not halt the program, so it’s sensible to put it in a loop to
wait until a key is pressed. When you press a key, the code of that key is
stored in the keyboard buffer, a type of temporary memory store. To make
sure that only the input you want is left in the buffer, you can clear it by
POKE 198,0 just before the GET loop.

It is also quite easy to ensure that any input is within the limits you set. A
program that only requires figures can use GET and check the code of keys
that are pressed. If any other key is pressed, the program can loop back to
request another input. This program does just that:

10 0 REM * *** * *** * * *** * * ** * * * ** * * * ** * * * *

110 R EM SE L E CT I VE INPUT R O UT I NE
120 E EM * * *** * ** * * ** * * ** * * *** * * *** * * ** *
130 P O K E 198,0
140 GE T A*:IF A$ = "" THE N 140
150 IF AS C ( A$ ) <48 OR A S C <A* )>5 7 T HE N P RI N T "NOT A

NUM BE R"
155 IF A S C <A* ) < 48 O R A 5 C < A $ ) > 57THE N GO TO 130
160 P RI NT "YOU PRE S SE D NU MB E R "A$
170 S TO P

READY.

Line 150 checks the ASCII code to make sure it lies between 48 (0) and 57
(9).

69

Programming for Education on the Commodore 64

A routine like this can also make a program easier for the user. One of
the most frustrating things for an inexperienced user is for error messages
to appear on the screen when they are half-way through the program.
Shielding the user from the operating system is an important area of pro
gramming, for, even if a program works perfectly, it can be spoiled by lack
of foresight on the part of the programmer.

Firstly, the program needs to be self-explanatory, as far as that is pos
sible. If someone puts a cassette in and presses SHIFT and RUN/ STOP,
instructions on use should be the first thing that appears after the title. If
the program is easy and pleasant to use, it is usually termed ‘user- friendly’.
If the program has several options, it is a good idea to make it menu-driven
to increase its friendliness. This means that a list of options appears on the
screen, and the user can make his selection from the displayed menu, eg

Press a number to choose:

1. Instructions

2. Easy Problems

3. Harder Problems

4. Difficult Problems

If any other key apart from 1, 2, 3 or 4 is pressed, the computer should
ignore it. This can be achieved by using a GET routine as explained earlier.

Another advantage is that the user does not have to press the RETURN

key.

In a program requesting the date of birth, INPUT can be used instead of
GET, but the manner in which the data is entered should be shown by an
example, then the input checked by the program.

1000 REM BIRTHDATE SUBROUTINE
1010 PRINT‘‘ENTER YOUR DATE OF BIRTH”
1020 PRINT‘‘USE THE FOLLOWING ORDER - ”
1030 PRINT‘*DATE, MONTH, YEAR”
1040 PRINT‘‘E.G. 4TH MARCH 1956 WOULD BE”

1050 PRINT” 4<RETURN >”
1060 PRINT” 3<RETURN>”
1070 PRINT” 1956< RETURN> ”

1080 PRINT* *DATE - ” ;
1090 INPUT DATE
1100 IF DATE < 1 OR DATE >31 THEN 1090

1110 PRINT*‘MONTH-
1120 INPUT MONTH

70

Chapter 4 Making Friends with your Keyboard

1130 IF MONTH < 1 OR MONTH > 12 THEN 1120
1140 PRINT“ YEAR-
1150 INPUT YEAR
1160 IF YEAR < 1880 OR YEAR > 1984 THEN 1150

The example suggests the entry format, so the user knows the correct order

of input, and also that he is expected to enter figures and not words.

If impossible dates, such as -4/15/1983, are entered, they are outside
the permitted range of inputs. If letters are entered, eg APRIL instead of 4,
the 64 generates an error message — REDO FROM START — so the input

loop is repeated once more. If the RETURN key is pressed with nothing

entered, the loop is also repeated.

The way to make the routine check that only figures are entered would

be to make the input lines contain string, rather than numeric, variables,
and check their ASCII codes. This would be a useful exercise for you to try.

In this chapter, we are including some programs that help children find

their way round the keyboard. They also introduce ideas that you may find
useful in your own programs.

Keyboard encourages fast entry of all the characters on the keyboard.

The instructions are presented as a subroutine and the TIME function in
the machine starts when the space bar is pressed. A large version of the
character appears on the screen and three attempts are allowed to find the
correct key.

In the 64, the character definitions are stored at memory location 53248

onwards. Each character on the screen consists of eight rows of eight posi
tions, like a chess board. Each row is represented by a binary number. If
you imagine a black character on a white background, then ones stand for
blacks, and zeros for whites, so a totally filled-in character would contain
255 in each row, as the binary code for 255 is 11111111.

On some computers, it would be easy to find the character definitions by

PEEKing the locations where they are stored. The 64, however, uses a
system that is more complicated, in order that more is available to the user.
It reads its character set from ROM which shares the same addresses as
user memory and some input/output routines. Every time the 64 needs to
display a character, a pointer in another part of the memory sends it to the
character ROM. If we want to read the definitions, or indeed to change the
set to display our own definitions, the easiest thing is to copy the entire
character set into user RAM (which can be altered). The 64 must also have
the pointer changed so that it points to the new character set.

The following program copies the character set from ROM into RAM at

location 12288. If this is all that is done, your BASIC program may over
write the new set at a later stage. The 64 must be told that it cannot use this
space, so the pointers to string variable space and the highest address used

by BASIC have to be changed. Then the keyscan interrupts have to be

71

Programming for Education on the Commodore 64

turned off and the 64 told to look at the character ROM rather than RAM.
At this point, all the necessary characters in the ROM can be scanned and
their definitions POKEd into their new locations in RAM.

If you were to halt the program at this point, you would find that the

keyboard had ‘died’. Even the RUN/STOP and RESTORE method
would not retrieve your program, as the keyboard is not being scanned.
With the characters in their new location, the thing to do is first to switch in
the input/output routines, then to start the keyboard scan routine. Now
that the character set is in user RAM, you can look at it easily, or alter it as
necessary.

Once the character definitions are available, it is possible to PEEK them,

and use the codes to produce large versions of them on the screen.

The way this is achieved is by storing the definitions in arrays that hold

the code for each line as a binary number; so 170 is stored as its binary
equivalent, 10101010. This number is now scanned. If a 1 is found, a solid
block is printed; if a 0 is found, a space is printed. This results in a character
sixty-four times normal area being printed on the screen. The actual pro
gram runs through the entire character set and prints the value held in each
location so you can see how the character is formed.

BigL

1000 R EM ** * L AR GE C HAR A CT E R P RO G RAM ** *
1010 R EM

1020 R EM *** M OV E C H A RA C TER SE T >RAM ***
1030 RE M

1040 P R I N T C H R $ (142)
1050 P 0 K E 5 2 ,48
1060 P 0 K E 5 6 ,48
1070 C LR
1080 P 0 K E 5 6 3 3 4 ,P EE K < 5 6 3 3 4 )AN D2 5 4
1090 P O K E 1,P EE K <1)A N D 2 5 1
1100 F O R I = 0 TO51 1
1110 P O K E I +1 2 2 88 , P E E K (I+53248)
1120 NEXT
1130 P O K E 1,P E E K (1)0 R4
1140 P 0 K E 5 6 3 3 4 ,P E E K (56 334)O R 1
1150 R EM
1160 R EM ** * P RI NT L ARG E L E TT E R S * **
1170 R EM
1180 Z = 1228 8
1190 P G K E 5 3 2 8 1 ,0

1 20 0 D I M B (8 ) s D I M C (8 ,8 )

1220 FO R X= 0 TO 511 ST EP 8
1230 P R I N T " LS H I F T/CL R / H O M E 1 "

72

Chapter 4 Making Friends with your Keyboard

1240 FO R N =0 T O7

1250 P RI N TZ+ X +N , P E E K (Z+X+N)

1260 B (N )= PE EK (Z+N+X)

1270 FOR J= 0 TO 7

1280 C<N ,J )= INT(B (N ) /2'*<7-J) )

1290 B ( N)= ( ( B(N ) /2 " ( 7-J ) > -C < N ,J) ) * 2 s <7~J)

1300 IFC < N ,J )=1 T H E N P O K E (10 6 4 + N * 4 0 )+15+J, 81s POKE

< 5 533 6 + N * 4 0 ) + 15 +J ,0
1310 NEX TJ
1330 NE X TN
1340 NE XTX

READY.

Commentary

Line 1040 clears the screen. Lines 1050 and 1060 tell the 64 where to store

strings and the BASIC program so that it won’t overwrite the new char
acter set.

Line 1070 frees all available memory space. Line 1080 turns off the key
board scan. Line 1090 selects the character ROM. Lines 1100 to 1120 copy
the contents of the first section of the character ROM into RAM. Line 1130
deselects the character ROM. Line 1140 turns on the keyboard scan. Line

1180 sets Z equal to the start of the location of the copied character set.

Line 1190 sets the background colour to green. Line 1200 DIMensions
space for the arrays necessary to hold large versions of the character
definitions.

Lines 1220-1340 contain the loop to go through the entire 64 copied char
acters. Lines 1240-1330 contain the loop to display each line of the
character.

Lines 1250 and 1260 store the decimal (normal) value of each line in a
variable, B(N).

Lines 1270 to 1310 contain a routine to convert the number in B(N) to its
binary equivalent. This is stored as a series of zeros and ones in array
C(N,J).

It can be seen, if you run this program, that it provides an introduction to
how a keyboard trainer program operates. In the next program, the char
acters are printed in a large version on the screen. These are presented to the

73

Programming for Education on the Commodore 64

user in a random fashion, and they have to input the correct letter from the

keyboard as fast as they can. If they are successful, another letter appears
and the time taken is added to their total time.

Keyboard

100 R EM *** KEY BOA R D T RA INE R ***
110 R EM

120 R EM *** A.J.S . 4/ 1 1/ 8 3 ** *
130 REM

140 REM ** * * ** * * ** * * * ** * * *** * * *** *
150 R EM
190 G OT O 1000 s REM MO VE C HAR A CT ER SET
200 GOS U B 30 0 0 :R E M I NS TRU CT IO N S
210 G OSU B 40 0 0 :R E M TE ST MOD UL E
220 GOS U B50 0 0:R E M SC OR E MO DU LE
230 GO TO 20 0
240 R EM

1000 RE M L AR GE C H AR A C TE R PRO GR A M

1010 RE M

1020 RE M R E LO C AT E C HA R AC T E R SET IN R AM

1030 REM

1040 PR I NT CH R$ <1 47 )

1050 P OK E S 2 ,48

1060 P 0 K E 5 6 ,48

1070 CLR

1080 P 0 K E 5 6 3 3 4 ,P E E K (563 34)AN D 25 4

1090 P O K E 1,P E E K (1)A N D 2 5 1

1100 F O R I = 0 T O 5 1 1

1110 POK EI + 1 228 8 , PE EK <I+53248 )

1120 NE XT

1130 P O K E 1,P E E K (1)0R4

1140 P 0 K E 5 6 3 3 4 ,P E E K ( 563 34 )O R 1

1150 GO TO 20 0

1990 RE M
200 0 R EM ROU TI N E TO P RI NT L AR GE L E TT E RS
2010 R EM
2020 Z = 122 88
202 5 R = I N T ( R N D (0)* 26)+ 1
2060 P RI NT CH R$<14 7)
207 0 F O RN = 0TO 6
209 0 B <N) - P E E K (Z +N+R*8)
210 0 F O RJ= 0TO 7
21 10 C (N , J ) = I N T (B < N ) / 2 ’* (7—J ) )

212 0 B(N) = <(B(N )/2 ’ ( 7~J ) ) - C < N, J ) ) * 2 S (7-J)

213 0 IFC < N ,J > =1 T H E N P O K E (10 6 4 + N * 4 0 ) +15 + J ,81

214 0 IFC < N ,J )= 1T H E N P O K E (55 3 3 6 + N * 4 0 ) +1 5+ J ,0

74

Chapter 4 Making Friends with your Keyboard

215 0
216 0
217 0

300 0
301 0
3020

303 0
3040

305 0

306 0

307 0

308 0

309 0

310 0

3110
3120

313 0

314 0

3150

316 0

317 0

400 0

401 0

4020

403 0

404 0

4050

406 0

407 0

408 0

409 0

410 0

411 0

412 0

413 0

414 0

415 0

416 0

417 0

50 00

5010

50 20

5030

50 40

505 0

50 60

507 0

508 0

509 0

NEX TJ
NE XT N
RETU RN
REM
REM *** I N ST RU CTI ON S * **

REM
P R I N T C H R * ( 147 ):P 0 K E 5 3 2 8 1, 5: P 0 K E 6 4 6 ,6
PRINT
PRIN T" YOU A RE A BO UT TO BE SHOWN"
PRIN T
PRI NT" 10 LE T TE R S A ND OT HER SYMB OL S"
PRIN T
PRINT" THAT AR E A LL O N T HE KEYBOARD "
PR IN T
PRI NT " FIN D TH E C OR R EC T KE Y A ND PRE SS"
PRIN T
PRINT" IT AS QU IC K LY AS YO U CAN"
FOR X = 1 TO 8: P RI NT : N EX T X
PRIN T" P R ES S THE SPA CE BA R TO GO"
GET Z*:IF ZS="" T HE N 3 16 0
RE TUR N
REM
REM *** T ES T M ODU LE ** *
REM
TS = TI M E:S C =0
FOR G= 1 TO 10
GO S UB 2 00 0
P 0 K E 7 B 2 ,5:P 0 K E 7 8 1, 20:SY S65 5 20
PR I NT "T HE L ET T ER IS

--------

>"5

P O K E 198,0
GET Z* :IF Z$="" T HE N 4 09 0
PR IN T Z$;

IF AS C ( Z$ ) =R+ 6 4 TH EN SC =S C+1
IF AS C (Z * ) =R + 6 4 TH EN PRI NT " YES"

IF A S C ( Z $ ) O R + 6 4 T HE N PRIN T" NO, "CHR* (R+ 64 )
FOR PA US E=1 TO 1 00 0: NE XT
NEX T G
T T = I N T ( (TI ME- TS)/60)
RE TU RN
REM
REM *** S CO R E M OD U LE ***
REM
PR IN TC HR *( 14 7)
PRINT
PR INT " YO U S CO RED "SC" CO RR EC T"
PRINT
PR INT " AN D T OO K "TT" S EC ON DS "
PRINT
PR I N T" P RES S SP AC E BAR TO G O AG AIN"

75

Programming for Education on the Commodore 64

51 00 GE T Z$ :I F Z$ = ,,M T HE N 5 10 0
52 00 RET UR N

READY.

Commentary

Lines 190-230 contain the control module.

Line 230 loops the program through the instructions and the test for as
many times as is necessary.

In order that the character set can be examined, it is copied from ROM in

the same manner as that used in the last program.

Lines 1000-1150 are responsible for the moving. When you RUN the pro
gram, you will have to wait for about ten seconds while this is achieved.
The subroutine is the same as the routine in BigL, so refer to that program

for more detailed notes.

Note that this is not a subroutine. If GOSUB 1000 is used in line 190, and

RETURN in line 1150, the program will stop with an error message in line

1150 (that there is a RETURN with no GOSUB). This is because the CLR in
line 1070 resets the stack containing the RETURN addresses.

The routine from line 2000 to line 2170 is also similar to that in BigL, and

is used to print a large version of the selected letter on the screen.

Line 2025 chooses this letter at random from the data.

Lines 3000-3170 contain the instructions.

Lines 4000-4170 contain the test module.

Line 4030 reads the current internal clock time into variable TS, and sets
the score counter, SC, to zero.

Lines 4090 and 4100 check the keyboard for an input, and lines 4110-4130
check this input against the selected letter. If it is correct, the score is incre
mented and YES printed.

Line 4140 provides a short pause so that the screen can be read.

After ten attempts, line 4160 is used to calculate how many ticks have been
produced by the jiffy clock, and this number is divided by 60 and rounded
off to produce the number of seconds taken.

76

Chapter 4 Making Friends with your Keyboard

Lines 5000-5200 contain the score module which simply clears the screen

(in line 5030) and prints the details of the test on the screen.

Masking

In the last program, and in one or two others, you may have found a parti
cular feature in a line that seemed to make little sense. A typical line might
be

POKE 56334,PEEK(56334)AND 254

It looks as though it means ‘ POKE a number with the number already there
plus 254’. This is not true, however, as AND is a logical operator, not the
same as +.

Logical operators are fairly easy to understand when they are used to

compare numbers.

10 INPUT“ A = ” ;A
20 INPUT“B = ” ;B
30 IF A = 1 AND B = 1 THEN PRINT “ YES” : GOTO 50
40 PRINT “ NO”
50 STOP

AND TRUTH TABLE

A B

0

0
0 1

1

1 1 1

0 ie FALSE
0 ie

FALSE

0 0 ie FALSE

ie TRUE — “ YES” printed

This program would print ‘YES’ if both conditions were true. If either or
both of them were false, it would print ‘NO’.

10 INPUT“ A = ” ;A
20 INPUT“B = ” ;B
30 IF A = 1 OR B = 1 THEN PRINT ‘YES’: GOTO 50
40 PRINT “ NO”
50 STOP

77

Programming for Education on the Commodore 64

OR TRUTH TABLE

A B
0 0
0 1 1

1 0 1

1 1 1 ie

0

ie

FALSE
ie TRUE
ie TRUE

TRUE

This program would print ‘YES’ if either of the two conditions were true
and the other were false, or if both of the conditions were true. If both the
conditions were false, then ‘NO’ would be printed.

When logical operators are used to compare numbers, which they can in
the range -32768 to 32767, then they compare the way the numbers are
stored in two bytes.

Bytes store numbers using binary digits, ie using only ones and zeros.

DECIMAL BINARY

0 0

1 1
2 10
3 11
4 100
5 101
6 110
7 111
8 1000

If two numbers are compared using AND, the individual bits of each
number are compared one by one, and the results are the same as in the
truth tables above.

Suppose the two numbers are 23 AND 254.23 is 00010111 in binary, and
254 is 11111110. Placing the numbers on top of each other and using AND,
we get:

00010111

11111110

00010110
You will notice, in the result line, the only bit to have altered is the last one

on the right. If the two numbers to be compared are 19 OR 4, the result is:

00010011

00000100

00010111

78

Chapter 4 Making Friends with your Keyboard

The technique of masking relies on this effect, to ensure that just one bit of
a number is set to a one or a zero. All the other binary digits remain the
same.

In the examples, it can be seen that, to ensure that the third bit from the
right is set to one, the number should be ORed with 4 (as 100 is 4 in binary).

To alter the fourth bit from the right, the number would have been ORed

with 8 (as 1000 is 8 in binary).

To ensure that the last bit on the right is set to zero, the number should be
ANDed with 255 - 1, ie 254. This is because the binary reverse of 1 is 254.
(Zeros instead of ones, and vice versa.)

One is 00000001 and 254 is 11111110. To alter the fourth bit from the
right, the number should be ORed with 255 - 8, ie 247. This is because the
binary reverse of 8 is 247. 8 is 00001000 and 247 is 11110111.

Why all this complexity to achieve such a small thing, you may wonder.
The reason is that, in order to use its memory carefully, several functions in
the 64 are controlled by single bits in a memory location, rather than by the
whole byte. There are several examples of this method being used in the
graphics and sound chips. For instance, location 53269 controls whether
the graphic characters called sprites are turned on. The eight bits of that
location each control one sprite. In a program, you might want to turn one
on and leave the others unaltered. The best way to do this is by ORing
location 53269; eg to turn on the first sprite, without affecting the others,
you would enter:

POKE 53269,PEEK(53269)OR 1

To turn it off without affecting the others you would use:

POKE 53269,PEEK(53269)AND(255 - 1)

79

CHAPTER 5

Story Time

Creativity — artificial intelligence — words at random — Story: a

program to help with creative writing and adjective use — interactive

use of computers — Gosh: more stories.

Can a computer be creative? To answer this question would take too long
in discussing the meaning of creativity and the future prospects of artificial
intelligence. At the end, there might not be any firm conclusions. What
would be agreed is that, given sufficient information, computers could
shuffle this information and display it in all possible ways, including some
that might appear creative and original.

For parents and teachers, the problem with children’s creativity is often
one of encouraging the child to start writing. Once the initial paragraph has
been written, the material begins to flow more easily.

The first program does not do anything that could not be achieved using
pencil and paper, but it does produce a result in far less time. Various
subjects and locations are held in DATA lines. If the user does not like the
combination selected, the program produces more at random when a key is
pressed.

The READ statement is a very useful feature of the BASIC language.
Instead of entering all the data during the running of a program, it can be
stored in DATA lines, usually placed at the end of the program. When data
is required, the statement READ is used, followed by a numeric or string
variable. When the program is RUN, a pointer moves along the DATA
lines, each time they are called. During the course of the program it is
possible to send this pointer back to the start of the DATA lines by using
the command RESTORE.

Enter this program if you aren’t sure about using READ, DATA and
RESTORE.

10 READ A

20 READ X$

30 READB

40 RESTORE

50 READ C,Y$,D

81

Programming for Education on the Commodore 64

60 PRINT A,X$,B,C,Y$,D

70 DATA 1,HELLO,37.5

Some BASICs allow you to RESTORE to a particular program line, but in
Commodore BASIC you have to resort to tricks if you want to use data

from the middle of DATA lines. For instance, to reach the fourth piece of
DATA you could have:

10 FOR LOOP = 1 TO 4

20 READ A

30 NEXT LOOP

40 PRINT A

50 DATA 1,2,3
60 DATA 4,5,6

Data can occupy several lines, and often looks neater in listings presented
in this way. The 64 sees it as one big block of data. Be careful you don’t
attempt to READ words into numeric variables, or you will get an error
message.

Story

In the following program, the child is requested to enter adjectives to des
cribe the subject and the location. On completion, the program produces
the opening paragraph of a story written around the data that has been
entered.

In terms of program complexity, this does not rank very highly, but it
does show the way in which apparently original text can be generated. It
also requires a lot of thought on the part of the child to enter suitable
descriptions that fit the mood of the opening sentence.

1000 REM *** STOR Y * **

1010 R EM
1020 REM *** AJS 9 /1 0/ 8 3 ***
1025 REM
1040 GO S UB3 0 00 : RE M GET WO RD S
1050 GO S UB4 00 0 :R E M PRI NT T EXT
1060 GOT O 10 40 :R EM L OOP P RO G RA M

202 0 REM
300 0 REM
301 0 R EM *** GET WO R DS ***
302 0 REM
303 0 RESTORE.
304 0 F O R N = 1 TO IN T(RN D (0)*5)+1

82

Chapter 5 Story Time

305 0 R EAD S TART#
306 0 NEXT
307 0 R ES TO RE
308 0 FQRN=1 TO 5 + I N T (R N D (0 )*20)+1
309 0 R EA D P ER S#
310 0 NEXT
311 0 R ES TO RE
312 0 F O R N = 1 TO 25 + 1N T ( R N D (0)*20)+1
313 0 RE AD P LA CE #
314 0 NE XT
399 0 R ET UR N

400 0 R EM

401 0 RE M *** WRITE I NTRO ***
402 0 RE M

403 0 P R I N T C H R # ( 14 7) s PRI NT n * Y OUR S T O R Y * " s PRI NT
404 0 P RINT S T A R T # ; " ";
405 0 P RI NT PE RS #
406 0 P RI NT " WA S SEEN NEAR"
407 0 P RI NT P LA CE #
408 0 P RINT
409 0 P R IN T "E N TE R 5 A D JE C TI V ES T HAT BEST D ESC RI BE "
410 0 P RI N TP E RS #
411 0 F O R N = 1 TO 5
412 0 INPUT PA DJ#( N)
413 0 N EX T Ns P RI NT
414 0 P R IN T "E N TE R 5 AD JE C TI V ES T HA T B EST DES CRI BE "
415 0 P RIN TP L AC E #
416 0 F O R N = 1 TO 5
417 0 INPUT LA#(N)
418 0 NEXT Ns PRI NT
419 0 P R IN T "P R ES S SP AC E BAR TO C ON TI NUE"
420 0 G E T Z#sI F Z # = " " THE N 4200
421 0 P R I N T C H R # (147)
422 0 P R I N T S T A R T # ;" ";PE RS #
4230 P R IN T" W AS S EE N N EA R "PLACE #
424 0 P RI NT" IF Y OU H AV E E VE R S EE N "PERS#
425 0 P R IN T "Y O U W IL L K NO W T HEY ARE " P A # ( D
4260 PR I NT " AN D " P A # (2)
427 0 P R IN T"T HIS ONE WA S A LSO RAT HE R " P A # (3)
428 0 P R IN T" A ND D ID N' T W AN T T O EN TE R "
428 5 P RI N TP LAC E#
4290 P R INT "W H ER E IT W AS "LA# <1)" AN D "L A # (2)
430 0 P RIN T "C E RT A IN L Y IT WAS NO P LA CE FOR"
431 0 P RI N TP E RS #
432 0 P R IN T"S OME CRE ATU RE S ENJO Y P LA C ES TH AT ARE"
433 0 P R I N T L A # (3)" AND " L A # (4)
4340 P RI N T" HO WE VE R, AN ADV EN TUR E HAS TO S TART "
435 0 P RI NT "S OME WH ER E, SO S OO N T HE " P A # (5)
436 0 P R IN T "F I GU R E OF "PE RS#

83

Programming for Education on the Commodore 64

437 0 PRI NT " CO U LD BE SE EN AB OU T TO EN TER"
438 0 P RI NT PL ACE*" W HI CH APPE AR ED "
439 0 P RI N T" E VE N MO RE " L A * (5)" T HA N B EFO RE"
440 0 P RI N TS PR I NT
441 0 P R IN T "P R ES S SP AC E BAR TO GO A GAIN"
442 0 GE T 2*sIF Z*="" T HE N 4 420
499 0 RET UR N
899 0 R EM
89 95 R EM *** O P E NI N GS ***
9000 D AT A ON CE UP O N A TI ME,A L ON G T IM E A GO
901 0 D AT A IN L ON G A GE S P AS T ,M A NY Y E AR S AGO
902 0 D ATA AB OU T 200 YE AR S A GO
9025 R EM * ** P E OP LE ***
903 0 D AT A A V ER Y O LD MA N, A Y OU NG GIRL

904 0 D AT A A ST RA NG E F IG URE ,A S HA M BLI NG V IS IO N
905 0 D AT A A BE A UT IFU L P R IN C ES S ,A W IC KED MAG IC I AN
906 0 D AT A A FI ER CE D RA G ON , A D AR K S TR A NG E R
907 0 D AT A A H A ND S O ME PR INC E, A HO OD E D FIGU RE
9080 D AT A AN E VI L W I TC H ,A M YS T ER I OU S VI SI TOR
9090 D AT A A LO ATH SOM E MO NST ER , A TE R RI FYI NG S HA PE
910 0 D AT A A SL IM Y T O A D ,A M AG IC S NA KE
911 0 D AT A AN E N OR M OU S W ORM ,A RE P ULS I VE A NI MA L
912 0 DATA AN E LE P HA N T ,A MO US E
913 0 R EM *** P L AC ES ***
914 0 DATA A D AR K F ORE ST , A DEE P C AVE RN
915 0 D AT A AN OLD C A S T L E ,A S HA DE D R A VI NE
916 0 D AT A A DEEP H OLE IN T HE G R OU N D, A HI DD EN MI NE
917 0 D AT A A DE SE RT ISLAND ,A TIN Y VI L LA GE

918 0 D AT A A H A UN TE D HO U SE ,AN EE RI E MA NS ION
919 0 D AT A A DA N GE R OU S M A R S H ,A L A RG E C OUN TR Y HO US E

920 0 D AT A A M YS T IC STONE CI R CL E,A N A R AB IAN BA Z AA R

921 0 D ATA A S TE A MI N G JU NG L E, A DE SER TE D TE MP LE

922 0 D AT A A LOS T C I TY , AN EM PT Y TOWN

923 0 DATA A BU RNI NG D E S E R T ,A S T EE P -SI D ED C AN YO N

READY.

Commentary

Lines 1040 to 1060 contain the control module. Line 1060 loops the pro
gram back to the start for a new story.

Lines 3000 to 3990 choose words at random. Line 3040 chooses an intro
duction from the first five phrases held in data. Line 3080 misses the first

five items of data and chooses a character at random from the next 20

items. Line 3120 misses the first 25 items of data and chooses a place at
random from the last 20 items.

Lines 4000 to 4200 print the chosen introduction and request the input of

suitable adjectives to describe the character and the place.

84

Chapters Story Time

Line 4220 onwards prints a framework of text in which the adjectives are

combined to make the first paragraph of a story.

Lines 9000 onwards contain the data lines. The data may be changed pro

vided the number of items in each section remains the same.

Gosh

After the last program, the time has come for a serious program to demon

strate the potential of the computer for creating original masterpieces.

Unfortunately, nothing of such high calibre was available!

We could attempt to disguise this program in educational language, to
make it seem highly motivating and wonderful at increasing cognitive
skills. When it comes down to it, however, it’s really just a lot of fun.

Gosh is a computerised version of Consequences, and expects inputs of
people, sayings, places and results. It contains some items in data, and
what it lacks in educational terms should be made up for by the amusement
it causes.

1000 REM BOSH - PAT HALL, JAM '84
1010 REM

1020 GOSUB

1030
1040
1050
1060
1070
1080
1090

1100

GOSUB
GOSUB
GOSUB
GOSUB
GOSUB
GOSUB
GOSUB

GOSUB 2430

1150

1250

1390

1530

1670

1810

1950

2090

m

■ REM

•

•

REM
s
5

REM PLACES
:

0

0 REM HER REPLY

0

0 REM
0

s

INITIALI SATION

MALE NAMES

REM FEMALE NAMES

REM

HIS SPEECH

THE CONSEQ UENCE
REM COMBINE AT RANDt
REM

PAUSE

1110 G OTO 1090
1120 END
1130 REM
1140 REM IN ITIA LIS ATI ON
1150 DIM MT < 15 ) s DIM FT ( 15)
1160 DIM PT< 15 ) : D IM ST < 15 )
1170 DIM RT< 15 ) : DIM C T ( 15 )
1180 R EM WH ITE SC REE N
1190 P OKE 53280, 1 : PO KE 53281, 1
1200 REM BL UE TEXT
1210 PR INT CH RT ( 31 )
1220 R ETUR N

85

Programming for Education on the Commodore 64

1230 REM
1240 REM MALE NAMES
1250 PR I NT M C SHI FT / CL.R / HOME 1"
1260 X = 7 : Y = 5 : GOSUB 2470
1270 PRINT "TYPE IN FIVE B OY'S NAMES"
1280 FOR I = 1 TO 5
1290 Y = 5 + I * 2 : GOSUB 2470
1300 GOSUB 2520
1310 MT( I > = AT
1320 NEXT I
1330 FOR I = 6 TO 15
1340 READ AT ; M T ( I ) = AT
1350 NEXT I
1360 RETURN
1370 REM
1380 REM FEMALE NAMES
1390 PRINT ""
1400 Y = 5 ; GOSUB 2470
1410 PRINT "TYPE IN FIVE G IRL'S NAMES"
1420 FOR I = 1 TO 5
1430 Y = 5+1*2: GO SU B 2470
1440 GOSUB 2520
1450 F T ( I ) = AT
1460 NEXT I
1470 FOR I « 6 TO 15
1480 READ AT : FT ( I ) = AT-
1490 NEXT I
1500 RETURN
1510 REM
1520 REM PLACES
1530 PRINT "C S HIFT /CLR /HOM EI"

1540 Y = 5 : GOSUB 2470
1550 PRINT "TYPE IN FIVE PLACES"
1560 FOR I = 1 TO 5

1570 Y = 5 + I * 2 : GOSUB 2470
1580 GO SUB 2520
1590 PT( I ) = AT
1600 NEXT I
1610 FOR I = 6 TO 15
1620 READ AT : P T ( I ) = AT
1630 NEXT I
1640 RETURN
1650 REM
1660 REM HIS SPEECH

86

Chapter 5 Story Time

1670 PRINT " I! SHI FT / CLR / HOME I "
1680 Y - 5 : GOSUB 2470
1690 PRINT" TYPE IN FIVE THINGS HE SAYS"
1700 FOR I = 1 TO 5
1710 Y « 5 + I * 2 : GOSUB 2470
1720 GOSUB 2520
1730 S T ( I ) = AT
.1.740 NEXT I
1750 FOR I = 6 TO 15
1760 READ AT : S T ( I ) = AT
1770 NEXT I
1780 RET URN
1790 REM
1800 REM HER REPLY
1810 PRINT " CSHI FT/C LR/H OME ]"
1820 Y « 5 s GOSUB 2470
1830 PRINT "TYPE IN FIVE REPLIE S MADE"
1840 FOR I = 1 TO 5
.1.850 Y =5+1 * 2 ; GOSUB 2470
1860 GOSUB 2520
1870 RT< I ) = AT
1880 NEXT I
1890 FOR I = 6 TO 15
1900 READ AT ; R T ( I ) = AT
1910 NEXT I
1920 RET URN
1930 REM
1940 REM THE CONSEQUE NCE
1950 PRINT " C SHIF T/C LR/H OME3 "
1960 Y = 5 : GOSU B 2470
1970 PRINT "TYPE. IN FIVE CONSEQUENCES "
1980 FOR I = 1 TO 5

1990 Y =5+1*2: GOSUB 2470
2000 GOSUB 2520
2010 CT < I ) = AT
2020 NEXT I
2030 FOR I = 6 TO 15
2040 REA D AT : C T < I ) = AT
2050 NEXT I
2060 RETURN
2070 REM

2080 REM COMBINE AT RANDOM
2090 PRINT "C S HIFT /CL R/HO ME3"
2100 GOSUB 2390

87

Programming for Education on the Commodore 64

2110 Y -• 7 s GOSUB 2470
2120 PRINT MTC N )
2130 Y = 8 ; GOSUB 2470
2140 PRINT "MET"
2150 GO SUB 2390
2160 Y =* 9 : GOSUB 2470
2170 PRINT F T ( N
2180 GO SUB 2390
2190 Y ” 10 s GOSU B 2470
2200 PRINT PTC N )
2210 Y - 11 ; GOSUB 2470
2220 PRINT "HE SAID TO H E R: "
2230 GOSUB 2390

2240 Y = 12 s GOSUB 2470

2250 PRINT STC N )

2260 Y - 13 : GOSUB 2470
2270 PR INT "SHE R E P L I E D : "
2280 GOSUB 2390
2290 Y == 14 : GOSUB 2470
2300 PRINT ETC N )
2310 Y •==• 15 s GOSUB 2470
2320 PRINT "AND THE CONSEQ UENCE WAS"
2330 GO SUB 2390

2340 Y = 16 : GOSUB 2470
2350 PRINT CT C N )
2360 RETURN
2370 REM

2380 REM PRODUCE RANDOM NUMBE R
2390 N = INTC RMDC 1 ) * 15 ) + 1

2400 RETURN

2410 REM

2420 REM PAUSE

2430 FOR I = 1 TO 6000 s NEXT I

2440 RETURN

2450 REM

2460 REM PRINT TAB ROUT IN E

2470 POKE 782, X s POKE 781, Y

2480 SYS 65520

2490 RETURN

2500 REM

2510 REM CHECK INPUT FOR LENGTH

2520 GOSUB 2470

2530 PRINT "

2540 PRINT "

88