Radio Shack TRS-80 Model 100 Basic Manual

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MODEL

LANGUAGE

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100

BASIC

LAB

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Model

100

BASIC

Language Lab

A DIVISIONOFTANDY CORPORATION

FORT WORTH, TEXAS 78102

Model 100 BASIC Language Lab Program:

Model

100

BASIC Language Lab Program Manual:

Reproductionoruse, without express written permission from Tandy Corporation,ufany portion of this manualisprohibited. While reasonable efforts have been taken in the preparationofthis

manualtoassure its accuracy, Tandy Corporation assumes liability resulting from any errors or omissionsinthis manual, or

from the useofthe information contained herein.

109

8 7 6 5 4 3 2 1

no

Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Lesson Lesson Lesson Lesson Lesson Lesson Lesson Lesson Lesson Lesson # 10 Data Files ' , Lesson #11Average Sales Lesson Lesson #13Function Keys Lesson Lesson

Application # 1 Calculator Application Application

Index

#1

Introduction to

#2

Saving Programs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...15

#3

Interest Calculations... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...31

#4

Sales Commissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...45

#5

Day, Time and Date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...57

#6

Using the Editor.

#7

Sales Trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

#8

Plot Your Data

#9

Functions

#12

Sound & Simulation

#14

Using the COM Option

#15

TELCOM Applications

#2

Memory Master Game

#3

Descriptive Statistics

BASIC.

"

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

.. ..

69 87

99 111 123 131 145 155 165 175

185 189

195

203

Introduction

If

you've used your TRS-80 Model 100 just once, you know how simple, versatile,

to

and powerful a computer it is. Its built-in application programs allow you normally complex computer operations with ease. This includes data manipulation, computer-to-computer communications, word processing, and more.

as

However, computer even more useful by customizing it to suit your own special needs. This done through BASIC, the built-in programming language.

For instance, from BASIC, you can:

• Re-define the Function Keys

• Communicate with information services and other computers.

• Write programs for a wide range performing interest or mortgage calculations.

• Make use

and a host This course will show you how

detail the BASIC section time you've finished this course. you'll be writing your own programs and using the

built-in application programs more effectively.

Since most

since BASIC interacts with the other built-in programs, you'll find it your advantage

you become more familiar with your Model 100, you can make the

(fj)

through

of

the computer's graphic and sound capabilities.

of

other operations!

to

perform operations suchasthese by explaining in

of

your Model 100 Owner's Manual. This means that by the

of

the application programs not built-in will be writteninBASIC, and

to

become familiar with BASIC.

(lID.

applications suchasforecasting sales trends and

is

perform

definitely to

is

So sit back and get ready to enjoy your Model out how powerful a computer it really

is!

100 even more. You're about to find

1

it'

Lesson

To use the BASIC capabilities of the Model 100, you must first learn how to communicate with your Computer. Essentially, this involves typing instructions on the

keyboard and watching the display for responses from the Computer. While you can type anything you wish on the keyboard, the Model 100 only responds

to words written in its own something which the Model with an error message.

In this lesson, you will learn a few BASIC commands Computer and write simple programs.

It should be mentioned at this point, that even when you type a BASIC word, the

Model keyboard) for processing by the Computer.

Throughout this Manual, the phrase "enter this command" will be used often. This simply means that you should press Also, when together.

100 will not respond until the ENTER key (located in the right side of the

#1

is

pressed. After pressing

we

tell youtopress

Introduction

"language." This "language"

100

to

BASIC

is

BASIC.Ifyou type

does not recognizeasa BASIC word, it will respond

to

communicate with your

(ENTER),

~

~,

the line just typed is placed in memory

after typing the command or instruction.

you should press both

(SHIFT)

and

(PAUSE)

Accessing BASIC

Priortotyping or editing a BASIC program, you must access the BASIC interpreter the Model 100.

When you Power-Up the Computer, you will see the Main Menu, which shows all the

''files'' that exist in the Model 100's memory. Think

file folders that may hold text or programs.

If

you haven't created any files, the Main Menu displays the built-in application

programs:

11:06:08

TEL

COM

20897

On initial Power-Up, the Main Menu Cursor - the large, dark rectangle - is positioned over the word word by pressing the Cursor Movement Keys

"BASIC."

The Cursor can be placed on any other Menu

«(3

of

these computer files simply

(C)Microsoft

ADDRSS

Bytes

, G , rn ,or rn).

free

of

as

3

To access the BASIC interpreter, simply position the Cursor over the word BASIC and press

CEmR.l.

The Display will then look like this:

TRS-8~

(cpr. 21190

Ok

The number 2119QIindicates the number of free bytes for creating any programs and

it may vary depending upon the capacity have been created and saved.

The word 0

Command Mode

Experiment

A commandisan instruction to the Computer ordering it todosomething

immediately. In this experiment you will learn how to enter a simple command.

First you will attempt to have the Model the name:

JOHN

Model

1983

Bytes

k and the flashing cursor symbol below it, indicate that you are in the

of

100

Software

Microsoft

free

of

your machine and whether any other files

BASIC and ready to begin programming.

#1

Entering a Command

100 print out a name on the display. Type

SMITH

You may use any other name. Now, press

Computer displays the message:

?8N

Error

This message indicates that an error, specifically a syntax error, has been made. The

syntax error occurred because the Computer doesn't recognize John Smith its vocabulary (also knownasthe Instruction Set).

The correct way to instruct the Computer to print the name

PRINTIIJOHN

Be

sure to press quotation marks enclosing the name are recognized as part vocabulary. This way no syntax error occurs and the name appears printed right below the command.

~

8MITH

at the endofthe line. The key word PRINT and the

II

~.

(ENTER)

As soon as you do this, the

as

is

to type:

of

the Computer's

part

of

4

PRINT "JOHN SMITH"

JOHN

Ok

SI'1

I

TH

•

Use the PRINT command to print your own name if you haven't already done so. Also, try printing other phrases. For example, to print How now brown cow, type:

PR

I NTIIHOW

Notice that the phrase is printed exactly as it appears within the quotation marks, including spaces.

NOW

BROWN

COWII(ENTER)

Experiment

A BASIC executes, one at a time, in a in

that it is precededbya line number.

Here is a simple BASIC program:

This program, consistingofonly one statement, the PRINT statement, accomplishes the same thing

But because the word PRINT is being used in a program and preceded by a line number, it is now called a statement. The number statement is called a line

number, even

Type line10as it appears above. Notice that nothing happens this time when you

press immediately, a program does nothing until the Computer is instructed to execute it. This is accomplished with the command:

Type the RUN command. After entering the RUN command, the program

programisa listofinstructions (or statements) that the Computer

10

PRINT

(ENTER).

RUN

#2

"JOHN

as

the command:

"JOHN

What is a BASIC Program?

sequential order. An instruction differs from a command

SMITH"

number.

CENnID

H'J

which is typed before the PRINT

Every lineina BASIC program must have a line

ifthe program contains only a single line.

Unlike a command, which instructs the Computer to perform a task

Don't

forget to press

(ENTER)

is

after typing it.

executed and the nameisdisplayed.

5

10

PRINT "JOHN SMITH"

RUN

JOI·-lNSMI

A more economical wayofinstructing the Computertoexecute your programisto press the RUN Function Key,

(ENTER).

Now

try

a slightly more ambitious program. Enter the following two-line program:

TH

~.

This accomplishes the same thingastyping RUN

10 PRINT

20

GDTO

The second statement in this program begins with line number 20, indicating that this instruction should

is

There thing instruction.

Execute the program with the RUN command or As

name within quotation marks repeatedly. This is known program because the GOTO statement in the second line of the program simply transfers control back to the first line which prints the and/or numbers) again on the next line.

Because of this continuous transfer, the program has

must be terminated manually by you. To

«(SHIFT)

When you press program stopped when it was "broken." For example:

nothing special about the line numbers used in this program. The important

is

that the PRINT instruction has a smaller line number than the GOTO

you can see, unlike the first single line program, this second program prints the

~).

"RADIO

SHACK

MODEL

100"

10

be

executed after the first line which has a smaller line number.

by

in

~,

pressing

no

"break"

the Computer will display a messagetoshow where the

10

the program, press

~.

as

an "infinite

"string"

wayofterminating and so it

(a group of characters

loop"

(BREAK)

6

Note that the program you wrote "scrollsupand off" the screenasthe program

If

began printing. command:

you wish to see the programasyou wroteitagain, enter the

LIST

or simply press the on the Display again.

List

10

PRINT "RADIO

20

GOTO

Ok

LIST

10

Function Key,

SHACK

CEID.

In either case, the program will appear

MODEL

100"

•

Execute this program again with the RUN command or by pressing (f!l. After letting This time after pressing

CONT

As

you can see, the program resumes execution. The CONT command is used CONTinue execution after the program has been same place where the program was interrupted.

the

program run a few seconds, terminate it by pressing

~,

enter the command:

"broken."

~.

Execution will start at the

to

Experiment

Here's the program from the previous experiment:

1121

PRINT

2121

GOTO

Suppose you want to change line10so that the message reads:

I

LOVE

This can be done by retyping line 10 entirely:

1121

PRINT

"RADIO

1121

MY

"I

#3

Simple Editing

MODEL

LOVE

SHACK

1121121

MY

MODEL

1121121"

7

1121121"

(ENTER)

Now, when you list the program with the LIST command or with the (f5) Function Key, the following is displayed:

10

2l2l

Ok

PRINT

GOTO

1l2l

"I

U)VE

MY

110DEL 101Zl"

•

Execute this programtoverify that the new phraseisdisplayed. Now, instead pressing program again. Pausing a program may be useful when you want displayed before it scrolls off view. pressing

Try a program:

Run this program. The output should

(BREAK)

to

(BREAK)

few

10

20

M\/

LEE

Ok

to

interrupt execution, press the

stop momentarily. To continue execution, simply press the

Of

course this program must still be terminated by

because it stillisin an infinite loop.

other experiments with the PRINT command. Type in the following

PRINT PRINT

NAJvIE

"MY "LEE"

IS

NAME

IS"

be:

(PAUSE)

key. This will cause the

to

read what is being

(PAUSE)

•

of

key

Now, retype line10to Also, add a semicolon

this

10

20

PRINT PRINT

"MY "LEE"

insert a space between the word

at

the endofline

NAME

IS

10.

The changed program should look like

";

8

"IS"

and the quotation mark.

Execute this program. The output should appear

MY

NAME

Ok

IS

LEE

•

as:

The printing appears all in one line because the semicolon instructs the Computer continue printing immediately after the first line is printed. The space after

was

the first line

If

you wantedtospace the name further apart, you could add more spaces after

or you could add spaces before Another way

10

line

Now list the program and it should read:

Run this program. The output should appear

so thatitreads:

10

LIST 10 20

Ok

added so that the words

"LEE"

to

space the printing istouse a comma insteadofa semicolon. Retype

PRINT

PRINT PRINT "LEE"

"MY

NAME

IS

"IS"

in line 20.

",

"

as:

and

"LEE"

would not run together.

"IS"

to

in

"IS"

NAME

This time line means "begin printing in the next field" (more on fields later).

"IS"

IS

and

"LEE"

L.EE

are spaced several columns apart. The commainthe first

9

Enter the following program:

1121

2121

PRINT PRINT

"HOW

",

"BROWN";

"NOW

"COW"

";

Would you guess what the outputofthis program will produce? When executed, the display will show:

Hm~

Ok

1\IOlr-J

BFWWI\ICOW

The comma in line10caused the two strings HOW and NOW to be spaced several columns apart. The semicolon between the two words

"BROWN"

and

"COW" caused themtoprint without a space. Nowifline10is retypedsothat the comma changedtoa semicolon and the semicolon at the end of the statementisomitted,

1121

PRINT

2121

PRINT

the output would

HOW

NOW

BROWNCOW

"HOW"; "BROWN";

be

"NOW"

"COW"

is

The second PRINT statement produces output on the second line because the carriage return after the first PRINT statement has not been suppressed with a semicolon or

If

comma. you could rewrite your program

you wantedtoprint the words on one line, neatly spaced one column apart,

as

follows:

1121 2121

PRINT PRINT

"HOW"; "BROWN";

"NDW

"CDW"

";

10

When it is executed, it produces,asexpected, the following:

NOW

BROWN

COW

A BASIC program can be edited a line at a time simply by retyping the entire line you have been doing.

To delete an entire line from a program, all you have

to

of the statement you wish

delete and press

~.

todoistotype the line number

For example, list the current program:

PRI NT PRINT

Now

type

20~

If

you list the program again, you will

"HOW "BROWN

"?

"NOW

";

"COW"

see

that line 20 has been effectively deleted:

as

1~

PRINT

"HOW";

"NOW";

Ok

I

Retype line 20 to restore your programtoits previous form:

10 20

PRINT PRINT

"HOW "BROWN

";

"NOW";

"j

"COW"

11

A

new

line can be added to a BASIC program at any time simply by typing it with the

If

appropriate line number. number less than

10

you wanttoadd

(the smallest line number allowedis1).Ifyou wanttoadd a line

between the two lines, give it a number between

10

Line numbers numbers had been used, for example inserted.

5).

It

and 20 were usedtoallow insertionofnew lines.Ifsuccessive line

15

is a good practicetouse line numbers that

a statement before line

10

and 20 (e.g., 15).

and 16, thennonew lines could have been

are

multiplesof10

Here's your program again:

10

20

PRINT PRINT

"HOW"j"NOW" "BROWN

II

j

"COW"

j

Suppose you want to insert a line between10and 20. Simply type:

15

PRINT

"SPLENDID

";

~

When you list the program now, it will show:

10,

give it a

(or at least

PRINT PRINT "SPL.ENDID PRINT

"HOW"; "BROWN

"NOW";

"i

!I;

"COW"

Even though line15was typed after lines10and 20, it takes its correct place in the

10

program because its line number falls between

and 20.

Execute this program. The following output will result:

NOW

SPL.ENDID

BROWN

COW

It should be clear by now that any BASIC program can be edited easily with the use

of

the line numbers. You can add, delete, insert, and change lines and that is all you

to

ever need

do.

12

Experiment

By

now you should be able to write simple BASIC programs using the two

instructions PRINT and GOTO.

#4

Writing Your Own Programs

Before you go on experimenting with the spacing comma and the semicolon, you should be aware NEW command.

When you enter the NEW command, any program that has been previously typed and

is

currently residing in working memory will be erased automatically.

Before you begin typing in a new program, you should always use the NEW

command to clear out the old program. Otherwise, you may end

combination Assume that your old program still resides in memory:

10 PRINT

is

20 PRINT

Now, without deleting this program, enter the following new program:

10 PRINT

of

your new and old programs.

"HOW";

PRINT "SPLENDID

"BROWN

"MY

";

COMPUTER

"NOW";

"; "COW"

IS

in PRINT statements using the

of

another useful command, the

-up

with a

A

";

20 PRINT "TOOL."

If

you list the program, you will find it

is:

LIST

10 15 20

PRINT PRINT PRINT

K

"MY

COMPUTER "SPLENDID "TOOL."

";

IS

A

";

Note that line15still exists because that line number was not usedinthe new program. command NEW. This won't be necessary, however, exists

So

remember, before typing a new program, clear the memory with the

if

you are certain that no program

in

memory.

What you have learned:

In this lesson you have learned some commandstowrite and execute a simple BASIC program. The PRINT and GOTO statements have been used to display simple messages. Editing a BASIC program can be typing new lines. The NEW command is used memory.

13

accompli~hed

to

deleteanentire program from

by retyping existing

line~

or

Lesson

In this lesson you will learn howtosave programs in memory and on cassette tapes. You will program with another program.

IJ.lso

#2

learn how to recall a program from storage and how to merge a stored

Saving Programs

Experiment

As

it was mentioned before, the Model 100 can hold several files, many9fwhich can

be

program files, In Lesson 1 you learned to write simple BASIC programsinthe BASIC system use repeatedly, it is a good idea Random Access Memory). When you save a program in RAM, in effect, you create a program file.

The following program serves to demonstrate how any program can be saved in RAM:

10 PRINT "THIS 20 PRINT

Access BASIC. Clear working memory with the NEW command and then type the

program

Execute the program, The following will be displayed:

asitappears above.

THIS

OF

Uk

1::'1

THE

#1

of

the Computer. When you have written a program that you intend to

"OF

A TEf3'T

MODEL

Saving a Program In

to

save it in memory (also knownasRAM, for

IS

A TEST"

THE

100

MODEL

COMPUTER

100

COMPUTER"

RAM

II

The first step for saving a program in RAMisto decide upon a filename. This filename appears listed as a file in the Main Menu and it serves to identify the program. Filenames cannot exceed six characters in length.

You may use any combination character in a filename must always be a letter. The following are examples filenames:

MYPROG

SKETCH ACCNT2

of

letters and digits for a filename. However, the first

of

15

valid

The following are examplesofillegal filenames:

1PROG MICROCOMPUTER

(must begin with a letter) (exceeds the maximum of six

name)

c,haracters in any file

Suppose you want to save the program above under the filename

PROG1

Todothis, simply type:

SAVE

IPROG1"

~

The Display will show the prompt OK to indicate that the program has been SAVEd.

Use the command NEW to clear the program from working memory. To verify that

the program no longer exists in working memory, enter the command:

LIST

or press

LIST

(ENTER)

~,

the LIST Function Key. The computer will respond with:

OK

and nothing else, indicating that there isnoprogram currentlyinworking memory.

It

The program has not been wiped out.

in

now exists

FILES

RAM. To confirm that thisistrue, enter the command:

(ENTER)

has been erased from working memory but it

or press the FILES Function Key,

the

file~

storedinRAM, including all BASIC programs, will be displayed. In this

if

case,

you haven't SAVEd any other programs or files, the name

®.

In responsetothis command, the namesofall

PROG1.BA

willbedisplayed.

is

This

your program. The that this file is a BASIC program. The Computer automatically appends this extension to the name

of

any BASIC program whenitis

If you want more proof that your program was indeed saved as a file, press the Menu Function Key,

CEB).

below.

Jun

22,1983

BASIC SCHEDL

Select:

characters"

.BA"

form a

"file

extension" which indicates

saved in RAM.

You will see PROG1.BA displayedinthe Main Menuasshown

Wed

10:34:17

TEXT

TEL

COM

PROG1.BA .

.....,...

21350

""'.

Bytes

---

free

16

A simpler way to save a program in RAM,isto use the SAVE Function Key, After typing a program you wish to save, simply press prompt you with the message:

~.

The Computer will

~.

Save

All you have to do thenisto type a name for the fileasyou did before and press

(illEID.

The numberoffiles which can be saved is limited only by the amountofRAM available.

up

used

Experiment

After you have saved a program in RAM, you may execute it simplybypositioning the Cursor over the word identifying it in the Main Menu and pressing

However,ifyou wish to modify or alter the program in any way, itisvery convenient to LOAD

Let's use PROG BASIC system.

You can do that with the command:

LOAD

Another way to LOAD the programisto pressing

Load

"

If

you continue to add files to RAM, eventually all available RAM will be

andnomore programs can be saved.

#2

it

into the BASIC system.

1 which you SAVEd in the last experiment and LOAD it into the

"PROG1"

~

the message

"

Loading a Program From RAM

(ENTERJ.

~

press

the

LOAD Function Key.

CE2l.

After

appears on the Display. All you shoulddothenisto type

PROG

1"

(ENTER)

After Loading PROG1 with the LOAD command or (f2), LIST the program to verify that it is indeed in working memory. The following should be displayed:

List

10

PRINT

20

PRINT "OF

Ok

"THIS

THE

IS

MODEL

A

TESTH

100"

I

If you execute the program with the RUN command you will see that the outputisthe

same

as

before.

Enter the command FILES or press

(11).

17

You will see that the program PROG1.BA is still listed, indicating that itisstill saved

in RAM, Loading a program from RAM does not erase it from storage. Notice, however, that an asterisk appears to the right of PROG1.BA. The asterisk

indicates that the program

Use the NEW command to delete the program PROGI from working memory. Use the LIST command to verify that working memory does not contain the program. Now type the command

RUN

"PROG1"

The following should appear on the LCD:

is

currently in working memory.

CEHnID

THIS OF

Ok

THE

IS

MODEL

A TEST

100

COMPUTER

11

This illustrates a useful optionofthe RUN command.Ifthe RUN command is

of

followed by the name quotes), then the program will be loaded into working memory and executed immediately. Thus the command:

RUN

"PROG1"

is equivalent to the two commands:

LOAD RUN

Use the LIST command to verify that the program now resides in working memory. The program will be modified by adding a third line. Type the following line:

30

List the program to verify that it

"PROG1"

CEHnID

PRINT

a program stored in RAM (the name must be enclosed in

00£!lID

mEID

"AND

ITS

is:

AB

I LI

TV

TO

STORE

FILES"

CEBllID

LIST

PRINT PRINT "OF PRINT

"THIS "AND

THE

ITS

IS

A TEST"

MODEL

ABILITY

100

TO

18

COMPUTER"

STORE

FILES

When you LOAD a program from RAM into working memory, you may add, delete,

or insert new lines as you wish. The changes you make are immediately incorporated

into the program. Delete the program from working memory with the NEW command. Use the LOAD

command to recall program

"PROGI"

from RAM. Type:

LOAD

List the program with the LIST command. You should

The new line was effectively incorporated in

"PROG1"

PRINT PRINT "OF PRINT

"THIS "AND

mEID

IS

THE

ITS

A TEST"

MODEL

ABILITY

see:

1~0

COMPUTER"

TO

STORE

FILES

"PROGI"whichisstored in RAM.

You can also LOAD and execute a BASIC program directly from the Main Menu.

(fI) to exit BASIC and return to the Main Menu. You should see something

Press similar to

(

C:>

jvli

Cl

....

[)!::·CJf·

Jun

!

SCHEDL

22.1983

Wed

.10=37:07

TEXT

TEL

PROG1.BA .

COM

(\

DD

i:~

:::\

t

~:j

21350

Bytes

tree

Move the cursor over the filename PROGl.BA as indicated below.

TEL..C()!V!

5CHEDL.

._0.

n

•...•

.••-II--

19

If

you press

loads and executes PROG1.BA. You will see

(ENTER),

several things will happen: the computer enters BASIC and then

THIS OF AND

Ok

THE

ITS

IS

MODEk

A TEST

1~~

ABILITY

COMPUTER

TO

STORE

FILES

•

with the Ok prompt indicating that you are in BASIC.Ifyou list the program you will see that PROGl.BA is in working memory.

Experiment

Itispossible to change a file name using the command:

NAME

where oldfilenameisthe nameofthe programasit now exists, and new filename the.

new program name you wishtoassign to it.

For example, if you wish to change the filename "PROG

NAME

Verify the name change with the FILES command orbypressing

"old

"PROG 1 •

#3

Changing a Filename

filename.extension"

BA"

AS

"TEST

"new

filename.extension"

1 •

BA"

(ENTER)

1"to"TEST!,"

CEf).

is

typc:

Now, using the NAME

NAME

Again, you may confirm that the name was changed to PROGI with the FILES command.

"TEST1.BA"

Experiment

Whileitis convenient to save your programs in RAM, thereisonly a finite amount space available. Eventually, there willbeno

An alternate method cassette recorder. Using cassettes, you can store essentially an unlimited number programs.

...

AS

command, change the file name back to

AS

"PROG1.BA"

#4

Saving a Program on Cassette

room left for new programs to be saved.

of

saving your filesisto store them on cassette tapes using a

20

~

"PROGl."

of

PROGI should still be in working memory. Use the LIST commandtoconfirm that it

It should appear

is.

as:

LIST

10

PRINT PRINT PRINT

If

it is notinmemory you should LOAD it from RAM or type itinas shown above.

"THIS

"OF "AND

THE

ITS

IS

A TEST"

MODEL

ABILITY

100

TO

COMPUTER"

STORE

FILES

To save a program on cassette, it is first necessary to connect the Model

suitable cassette recorder. For optimum results

we

recommend the Radio Shack

100 to a

CCR-81 Computer Recorder (catalog number 26-1208) with connecting cable and

instructions supplied. Be sure that the proper connections are made before proceeding further.

Place a blank tape in the cassette recorder and rewind it,

if

necessary. Then advance the tape past the leader. (If you use Radio Shack Leaderless cassettes, catalog number 26-3019, this isn't necessary.)

Press the RECORD (red key) and PLAY keys down together. They should stay down, but the tape will not move.

If

it does, youdonot have the remote jack inserted. Insert

the jack. Now you are ready to save the program onto the tape. Enter the following command:

CSAVE

"PROG1"

The recorder will run briefly and then stop. The RECORD and PLAY keys, however, will stay down. After the tape stops, you may press the STOP key and rewind the tape.

1.

The program now has been saved with the filename .'PROG

to

Another way

save the program on tape, insteadofusing CSAVE

"

"PROG1"isto

use the command:

SAlJE

"CAS

:filename

II

where CAS: specifies the device to be used for the saving operation,inthis case the cassette recorder, and filename

is

the nameofthe program to be saved. Using this

command, you would specify:

SAIJE

"CAS:

PROG

1"

~

21

Experiment

#5

Loading a Program from

Cassette

The program you just saved on tape in the previous experiment, PROG1, will now be loaded back into working memory. But first, delete PROGI from working memory with the NEW command.

Verify that it has been deleted with the LIST command or Function Key,

Be sure that the cassette recorder is properly attached to the Computer. Insert the

cassette containing the program into the recorder and rewind

Press PLAY on the recorder. The key will stay down, but the tape will not advance. Enter the following command:

CLOAO

As soonasyou press into the Computer.

FOUI\ID:

Ok

If

the tape was not read successfully, an displayed. the CLOAD command again to read the tape.

~.

"PROG1"

(ENTER),

If

thisisaccomplished successfully, the computer will display:

Pf{OG

1

If

this happens, rewind the tape and adjust the volume control. Then use

the tape will start turning and the program will be read

110

(InpuUOutput) error message will be

by

pressing the LIST

if

necessary.

If the tape is read successfully, you may verify that the program memory by listing it with the LIST command (or with displayed:

LIST

10 PRINT

20

PRINT "OF

30

PRINT

Ok

"THIS "AND

THE

ITS

IS

A TEST"

MODEL

ABILITY

10m

COMPUTER"

TO

~).

STORE

The following will be

FILES

•

22

is

in working

When the command CLOAD until a program stored under the name into working memory.

The command

"PROGI"is entered, the Computer searches the tape

"PROGI"is found. This programisthen read

LOADIICAS

may be used in place of CLOAD "filename". Remember that filename specifies the name

of

the program you wish to LOAD from the cassette.

Delete the program from working memory with the NEW command and verify that it

has been erased by using the LIST command.

Rewind the cassette and press the play key. This time type the command:

CLOAD

When this commandisentered, the cassette recorder will run briefly and then stop. Also, the computer will display:

FOUND:

Ok

:jilename"

COOfR)

PROGl

(ENTER)

II

indicating that the program was read successfully. List the programinmemory with the LIST command. You will see that the same program was loaded from the tape.

This illustrates another option program is omitted, the first program encountered on the tape Since your program PROGI was the first program on the tape, it was loaded into the Computer.

Experiment

Your Model 100 allows you to verify that a program has been saved successfully (i.e. without any errors) on cassette tape. Another option to accomplish this.

#6

of

the CLOAD command. When the filenameofthe

is

loaded into memory.

Verifying a Stored Program

of

the CLOAD commandisused

23

Verify that the program still resides in working memory with the LIST command.Ifit has been deleted, load it from the cassette tape or type it in from the keyboard. Here is

the listing again:

LIs'r

10

PRINT

20

PRINT "OF

30

PRINT

Rewind the cassette tape containing the program and press the PLAY key on the

recorder.

Type the command

"THIS "AND

THE

ITS

IS

MODEL

A TEST"

100

ABILITY

COMPUTER"

TO

STORE

FILES

CLOAD?IIPROG

The recorder will run briefly and then stop. The Computer will display:

Found:

OK

In this case, the program stored on tape was not SAVEd into working memory, but was compared, character by character, with the program already in working memory.

If

an inconsistencyisfound at any point, an error message will be displayed, indicating that the prugram working memory.

If

an error has occured, you can reSAVEthe program and use the CLOAD? command again to check the saved program.

As

with the CLOAD command,ifthe file name is omitted from the CLOAD? command, the first program encountered on the tape is compared with the program in working memory.

List the program in working memory. You should see:

LIST'

10

PRINT PRINT "OF PRINT

PROGl

"THIS "AND

1"

(ENTER)

saved on the cassette tape

IS

A TEST"

THE

ITS

MODEL

ABILITY

10121

was

COMPUTER"

TO

STORE

not the sameasthe one in

FILES

,

24

7

Delete line 30 by entering the line number. Now list the program to verify thatitis:

List

10

PRINT

20

PRINT "OF

Ok

"THIS

THE

IS

MODEL

A TEST"

100

COMPUTER"

I

Thisisnot the program that was saved on the cassette (line 30ismissing). The

be

CLOAD? command will program saved on cassette. Since they are not the same, an error message will be displayed.

Rewind the cassette and press the play key. Enter the command

CLOAD?

This time, the message:

usedtocompare the program in working memorytothe

Verify

will be displayed, indicating that the two programs are not the same. Don't forget the question mark (?) after CLOAD since otherwise the program saved on

tape will CLOAD? command indicates a can be used again to resave it.

be

Experiment

Rewind the cassette tape containing the saved program and press the PLAY key. Then load the program back into memory with the CLOAD command. List the program to confirm that it

LIST

10

20

30

failed

loaded into working memory, replacing the resident program there.Ifthe

#7

is:

PRINT PRINT "OF PRINT

~THIS

"AND

"bad"

Merging two Programs

IS

THE

MODEL

ITS

program on tape. then the CSAVE command

A TEST"

100

COMPUTER"

ABILITY

TO

STORE

FILES

25

The program will now be savedinRAMin"ASCII"

"compressed" format. This means that the program will be saved exactly

format, rather than the usual

asitwas

written. Ordinarily, programs are saved in compressed form.Incompressed form, key

as

words such

PRINT, are replaced by a single charactertoconserve storage space.

Type the following command:

The

SAVE

"A"

"PROG2"

tA

(ENTER)

following the name indicates that the programistobesaved in ASCll

mode.

to

Another way of saving a program in ASCII format, is

to

of the SAVE command. For example,

SAVE

"PROG2.00"

CEJIIER)

SAVE PROG2 in this way you could type:

use the extension .DOaspart

Delete the program from working memory with the NEW command. Confirm that it has been saved in RAM with the FILES command. PROG2 will be listed

PROG2.00

The extension

"DO"

with the ASCII option. There are several reasons why you might want

as:

(for DOcument) will be attachedtoany BASIC program saved

to

save a file the ASCII format. As it will be illustrated later in this experiment, merging files is one of the main ones.

Delete the program from working memory with the NEW command, and type the following one line program.

S

PRINT

"HELLO

MODEL

100

USER"

(ENTER)

Merge PROG2, which is saved in RAM with the ASCII option, with this one line program, by typing the command:

in

MERGE

List the program in working memorytoconfirm that it

S 10 20 30

Merging a programinworking memory with one that only be done

PRINT

PRINT PRINT PRINT

if

"PROG2"

(ENTER)

is

"HELLO

"THIS "OF "AND

THE

ITS

MODEL

IS

A

MODEL

ABILITY

100

TEST"

100

USER"

COMPUTER"

TO

STORE

has

FILES"

been savedinRAM, can

the programinRAM was saved with the A (ASCll) option.

Delete lines 20 and 30 by entering just the line numbers and then rewrite line

follows:

10

PRINT

"HERE I S A MESSAGE

26

FOR

YOU"

(ENTER)

10

as

List the program in working memory to confirm that it

LIs·r 5

PRINT

10

PfHNT

Ok

PROG2 will now be merged with this two line program. Remember that PROG2isin RAM and consists

10

PRINT

20

PRINT

30

PRINT

"HELLO

"H[RE

of:

MODEL

IS

100

A MESSAGE FOR YOU"

"THIS IS A TEST" "OF

THE

MODEL

"AND

ITS ABILITY

USER"

100

TO

is:

COMPUTER"

STORE

FILES"

Note that the program in working memory and PROG2 both have a line

two programs with the command

MERGE

List the program.Itwill

•.

1::::([

5 PRINT "HELLO

Line10of resident in working memory. This will always happen. MERGEd have any line numbers RAM will replace the lines

Programs saved on cassette tape may also be merged with a program memory

CSAI,JE

"PROG2"

P RI

f\IT

"Ti-n~3n':; A

PRINT PRINT

the program (PROG2) saved in RAM replaced line10of the program

as

longasthey are saved with the A option. The appropriate command

"OF

","1\.10

"PROG2"

CENTER)

be:

MODEL

THE

ITS

of

the program in working memory.

100

USER"

lEST

"

MODEL

A:BH

in

100

COMPUTER"

..

ITY

TO

common, the lines of the program SAVEd in

tA

STORE

If

FILES

two programstobe

in

10.

Merge the

working

is:

or

SAVE

"CAS:PROG2"

tA

27

Then, to merge a program in working memory with one stored on tape, use the command:

MERGE

Once you have MERGEd PROG2 with the program in working memory, SAVE the newly formed program in the conventional way (without the A option) using the

SAVE "PROG

If

you returntothe Main Menu by pressing

have been SAVEd:

.-

-

-.

-

Se

Experiment

Often times you'll need to eliminate files and programs that are no longer useful, or

that you have SAVEd on tape

"CAS:PROG2"

1"

22,1983

-

·

-

·

-

·

--

·

:

lec:t

CEtll'EB)

command.

~,

Wed

11:~1:52

TEXT

PROG1.BA PROG2.BA .

.-

-

·

..

-

·

._.

--

·

_.

.-

·

#8

Deleting a file from

to

TEL

COM

-

·

._

.

.-

·

_.

..

-

·

.-

--

·

2fZJ8t:,<:1

free additional memory space.

you will see the two programs that

(C)Microsoft

ADDRSS

_.

.....

·

--.

-

·

...

.-

·

._-

..

-

·

:B~tes

RAM

You can delete a file from the RAM storage area with the KILL command. The

of

general form

K

ILL

where filename is the nameofthe program you wishtodelete, and extension specifies the characters .BA, in the case SAVEd with language program.

Use the KILL command

KILL

The prompt Ok and the blinking cursor will appear on the Display after the program has been deleted.

Use

the FILES command (or that PROGl.BA is no longer listed. This is because the program has been deleted from RAM.

To summarize, the KILL command deletes a file from RAM storage. The NEW command deletes a program from working memory, but does not affect the file in

RAM storage.

the KILL commandis:

"filename.extension"

of

a BASIC program, .DO, in the caseofa program

the

A option or a text document, and .CO,inthe caseofa machine

to

delete PROG1 from RAM:

"PROG 1 •BA"

CENTER)

(fj))

to

list the files in RAM storage. You will notice

28

Also, you should be aware that a file cannot be deletedifthe same file is also in working memory. That is,ifyou LOAD a program from RAM into working memory and then attempt to KILL this file, you will get an error message. You should first delete the program in working memory with the NEW command and then proceed to KILL the file in RAM.

What you have learned:

You have learned how to SAVE BASIC programs in RAM and on cassette tape. You learned how to LOAD a program from RAM or from tape and how to verify that a program has been saved correctly. You also learned how to MERGE a SAVEd . program with a program in working memory. You found out that in MERGE operations,ifline numbers in RAM are in common with line numbers in working memory, the line numbersofthe RAM file take precedence over those in working memory. Finally, you learned how to delete files from working memory and from

RAM.

29

Lesson

This lesson illustrates the useofvariables and the assignmentofvalues to variables. Applications to the calculation examples

The programs used in this and all the following lessons will be explained line to give you a thorough understanding

of

#3

the useofvariables in BASIC programs.

Interest Calculations

of

interest and mortgage payments will serve as useful

of

the operations and the concepts involved.

by

line

Experiment

If

P dollars are borrowed at the simple interest rater,then the amount S that must be

repaid after

S is called the sum and P is the principal. The first program in this lesson calculates S for the following values

CarefUlly enter the following program into the Computer:

After the program is entered, execute it by entering the

RUN

t years is given

S =

P(l

P = $10,000

r = 18%

= 10 years

t

P

10

2

3

L10 50

Function Key, (fj).

THE

Ok

III III

=

R

=

T

=

5

=

PRINT

SUM

+ rt)

per

1111000

•

18

10

P

IS

#1

year

( 1

*

"THE

$

Simple interest

by

the fonnula

ofP,rand

+ R

SUM

The

28000

t:

T>

*

$"

IS

output from the program should

;

5

RUN

commandorpressing the

be:

•

If

$10,000 is borrowed for 10 years at the simple interestof18%, you will have to

pay back

$28,000.

31

How the simple interest program works:

Line18assigns the valueof10000 to the variable P. This is called an assignment

statement.

assigned to it. Note that the principal, $10,000, is written without the dollar sign ($) or

comma (,). In general, numeric constants shouldbewritten without

dollar signsinBASIC.

The letter P is called a numeric variable because numerical values can

commas

be

or

Line28assigns the valueof.18 the 18% interest rate. The conversion to decimal form is necessary because BASIC does not allow numeric constants to be written with a percent

Line

38 assigns the value

allowed to repay the loan.

Line48computes the

Note that the expression,

P *

(1

+ R *

looks very much like the formula previously seen for calculating the sum.

"*,,

is used to denote multiplication and, as usual, + denotes addition.

Line58printsanexplanatory message and the valueofS. The variables

variable can be

a) any letter b) any two letters

c) a letter followedbya number.

For example, the following are all valid numeric variables:

A

But the following are not valid numeric variables:

P,R,T and S are all valid examplesofnumeric variables. A numeric

or

AA

sumofprincipal and interest and assigns it to the variable S.

T),

B2

to the variable R. This is the decimal equivalent

(%) symbol.

of

10 to the variable T. This is the lengthoftime (10 years)

The

CQ

Y9

symbol

of

IS

The ftrst four linesofthe program are assignment statements. In general, an assignment statement follows the form:

$5

A?

variable = expression

where "variable" is any valid numeric variable and "expression" is any valid

The

numeric expression.

expression is assigned to the variable.

The

arithmetic operators in BASIC are:

right hand side canbea constant. The valueofthe

+ addition

subtraction

*

I

"

multiplication division exponentiation

32

Line 40 contains an exampleofa valid expression containing arithmetic operators. Here are some more:

a) A*B/C

b) Q

c)

+ A4 - 6.5

F * H8 + J9

You should note that spaces this type. For example, the expression in a) could have been written

A*B/C This allows you However, it is important to note the order in which expressions such as c) are

evaluated. In BASIC, mathematical operations always follow a hierarchical order. Exponentiaton

has the highest priority, multiplication and division are next, and finally. addition and subtraction have the lowest.

Therefore, expression c) above, is interpreted to

J9."

However, if you wanted to add H8 and J9 together before multiplying their

sum times F, you would have to place parentheses around H8

F * (H8 + J9)

In this case the addition is performed first because the operation inside the parentheses is

carried out before the outside multiplication.

Multiplication and division have equal priority and will right. The same is trueofaddition and subtraction.Ifyou look at line 40 again

40 S = P *

it should be clear that the parentheses are needed. However, inside the parentheses, the expression:

or A*B / C or

to

space out the symbols so that they can be easily read.

(1

+ R *T)

or

blanks are not significant in arithmetical expressions

A * B/C

as

"the

productofF times H8 is added

+ J9:

be

performed from left

to

of

+ R * T

1

is

calculated correctly because the multiplication has higher priority than addition.

Experiment

If

you invest P dollars at an annual interest rate r, compounded k times a year, then

t years, your investment will have grown to the amount

after

S =

PO

A program will be written to calculate the value

other variables:

Pis

$ 5,000

r is 12% per year tis

5 years

k is 4 (i.e. interest is compounded 4 times a year.)

#2

+ r/k)tk

Compound Interest

of

S, for the following valuesofthe

33

S:

Enter the command NEWtoclear the previous program from memory. Then type the following program:

P

10 20 30

40

50 80

After the programisentered, execute it by entering the RUN commandorpressing

~.

The output frum this program will be:

=

R

=

T

=

K

=

S

=

PRINT

5000

.12

5

4

P

*

"TOTAL

( 1

K)

~

$"

(T

;

S

+

R /

IS

K)

*

TOTAL

Ok

IS

$

9030.5561733465

•

Even though the totalissupposed to represent dollars and cents, the computer has

to

displayed the number with 14 significant digits, including 10

of

decimal place (because this is the precision BASIC). You will see later how to display numbers in dollars and cents format.

The expression in line

P *

(l

+ R /

uses addition, multiplication and exponentiation operators. The exponentiation operator

has the highest priority and will be performed before multiplication or division and course before addition and subtraction. Becauseofthis priority, it was necessary to place parentheses around the exponent

T*K

Otherwise, the computer would have calculated

50

K)'(T*K)

numeric variables in Model 100

the rightofthe

of

P *

(l

+ R / K) A T

and then multiplied this expression by K.

Experiment

#3

Compound Interest with

Keyboard Input

If

you wantedtorun the compound interest program with different values for the variables, you would have to retype the appropriate lines in the program. Obviously that isn't very practical, specially values.

if

you just wanted to figure the interest for several

34

It

would be more convenientifyou could simply type in the values for the variables

as

the program is being executed.

The program will be changed so that the value for P, the principal, can be entered

as

during execution. The values for the other variables will be assigned, assignment statements.

Change line10to

10

PRINT

"ENTER

.

THE

PRINCIPAL";

before, with

and insert line

15

List the program to verify thatitis:

10

15

20 30 40 508= 60

Execute the program. When the program executes, the following message (called a

displayed:

ENTER

and the computer will wait for youtoenter the value for P. When a value for P is entered, for example Be sure to press

Here is what the output looks like:

ENTER TOTAL

15

INPUT

PRINT

INPUT

R = •

T = 5

K = 4

P

"ENTER P

12

P * (1 + R /

PRINT

THE

CENTER)

THE

18

THE

PRINCIPAL";

"TOTAL

18

K)h(T

$";

*

K)

8

PRINCIPAL?

5000, the program will executeasbefore

after typing the amount for P.

PRINCIPAL?

$

8030.5561733465

5000

"prompt")

and

print out the total.

will be

Line

10 prints the prompt message. The semicolonatthe endofthe line suppresses

so

the carriage return

Line

15 is the INPUT statement. When this statementisexecuted, a question mark printed and the computer will wait for youtoenter a number from the keyboard. After you type the number and press which appears after

The remainderofthe programisthe sameasbefore.

If

the semicolon is left out in line 10, then the question mark and the number you type

be printed on the next line below the prompt.

will

that the next character printed will be on the same line.

(ENTER),

INPUT.

the number willbeassignedtothe variable P

35

is

Experiment

The

INPUT.

value

printed without using a separate PRINT statement.

Delete line

statementisusually preceded by a prompt messagetoremind you what

to

enter.

15

10

INPUT

#4

An

optional formofthe INPUT statement allows the prompttobe

(by entering just the line number

"PRINCIPAL";

Another Way to INPUT

P

15)

and retype line10as

follows:

This single line is equivalenttothe previous lines10and will be printed immediately followed by a question mark. Then the Computer will wait for you to enter the value for P. The ending quotation mark must be followed a semicolon, a comma cannot be used.

It

List the program.

10

INPUT

20

R = •

30

T

40

K = 4

50

S = P *

60

PRINT

Execute the program. The following output occurs when you type 1000 for the principal:

PRINCIPAL7

TOTAL

Ok

should read:

"PRINCIPAL";

12

;;;

5

"TOTAL

IS

$

(1

+ R /

1000

1806.1112346693

IS

K)~(T

$";

P

*

K)

S

15.

The word PRINCIPAL

II

by

Run the program several times, entering different values for

Experiment

#5

Compound Interest with More

the

principal.

Keyboard Input

In this experiment, the compound interest program will be changedsothat the rate, wellasthe principal, can be input from the keyboard.

20

Delete line Retype line

10

by entering just the line number.

10

as:

INPUT

"PRINCIPALtRATE";

36

P t R

(ENTER)

as

Now list the program to verify that it is:

10

INPUT

30

T = 5

110

K = II

50 S = P * (1 + R /

60

PRINT

When you execute this program, the following prompt willbedisplayed

"PRINCIPAL, RATE";

K)h(T

"TOTAL

IS

$"

j S

P,

R

*

K)

PRINCIPAL,

In response, you should enter two numbers separated by a comma. For example:

PRINCIPAL,RATE?

and again the amountofthe investment will be printed. The complete output will be:

This program illustrates another optionofthe INPUT statement. Values for more than one variable can be assigned with a single INPUT statement. The variables should be

separated by commas and listed after the prompt. When the INPUT statement is executed, you must type a value for each variable, separating the values with commas. After the last value has been typed, you should press

Two separate INPUT statements could have been used, the first for the principal P and the second for the rate R as follows

RATE?

2000,

RATE?

3979.577"7269318

20lc10,

.111

.14

(ENTER).

113

INPUT

213

INPUT

However, it is more convenient to use just a single statement as was done in the program.

Experiment

"PRINCIPAL"; "RATE";

#6

R

Compound Interest with All

P

Variables Input

The previous program will be rewritten so that the values for all the variables can be entered from the keyboard. The program will also be changed so that it will not terminate after the total is printed. Instead, the program will ask again for values for the variables so that the amount different values.

of

the investment can be calculated for any number

37

of

s

Delete line 40 by entering just the line number and retype line 30asfollows:

30

INPUT

Then add two new lines:

70

PRINT

80

GOTO

"TIME,

(ENTER)

10

~

NUMBER

OF

PERIODS"

iT,

K

~

List the program to verify that it

INPUT

10

INPUT

30 50

5

60

PRINT PRINT

70

GOTO

80

The program will prompt you for values for all four variables, Hereisan example the outputofthe program with the following inputs:

PRINCIPAL,

TIME,

TOTAL

PFHNCI

The program will continue to ask for values for the variables until you terminate the program manually by pressing

"PRINCIPAL, "TIME,

= P

*

"TOTAL

10

NUMBER

IS

$

PAL.

( 1

RATE?

3979.5777269318

RATE?

NUMBER R /

+

IS

OF

PERIODS?

(BREAK).

is:

$"

2000,

RATE";

OF

K)"(T

;

5

.i

P,

PERIODS";

K )

*

L

5,

4

R

T,

K

of

Line18prints a prompt and allows youtoenter values for the principal P and the rate

Line 38 prints a prompt and allows you to enter values for the time T and the number of

Line principal and interest at the endofT years.

Line output so that it doesn't run together vertically.

Line

allows you to input a variety

command each time.

R.

periods K. Lines 10 and 30 could have been combined into one line if desired.

68

prints out the message

78

skips a line on the display after the output from line 60. This spaces the

88 transfers control back to line 10, where the program starts over again. This

"TOTAL

of

values for the variables without entering the RUN

IS

$"

38

and the value

of

S, the total

of

Experiment

#7

Printing a Name

·Personalizing the Output -

The compound interest programasit currently exists

10

INPUT

30

INPUT

50

S = P *

60

PRINT

70

PRINT

80

GoTo

Add line 40asfollows:

£10

INPUT

and change line 60

60

PRINT

Add line

List the programtoconfirm it

65

1121 3121 £10

50

PRINT

INPUT INPUT INPUT

S = P *

60 PRINT 65

PRINT

7121

PRINT

80

GoTo

"PRINCIPAL, RATE";

"TIME,

(1

"TOTAL

10

"NAME";

to

"TOTAL

N$;"

NUMBER

+ R /

IS

N$

FOR

IS

$";

is

Klh(T

$";

"

S

OF S

"PRINCIPAL, RATE"; "TIME, "NAME";

(1

"TOTAL

N$;"

NUMBER

N$

+ R /

FOR"

IS

$";

OF

K)h(T

S

1121

PERIODS";

*

PERIODS";

*

P,

Kl

1',

K)

is:

R

T,

K

R

T,

K

When you execute the program you will be prompted,asbefore, for the principal,

of

rate, time and number this data is entered, the name and the amount of the investment will the program and enter the data name you wish):

PRINCIPAL, TIME, NAME? TOTAL

Execute the program several times with various numeric values and names. To tenninate execution,

Lines

ut

NUMBER JANICE

IS

. 38 allow you

periods. In addition, you will be prompted for a name. After

be

as

indicated below (of course, you may enter any other

RATE?

$

17618.22531759

(BREAK)

2000,

OF

PERIODS?

SMITH

must be pressed.

to

enter values for the numeric variables in the program.

.13

39

10,

2

printed. Run

Line40is another name instead This variable, N$, is an example example.,

Line

JANICE

58 calculates the total

of

a number.

SMITH,

INPUT

statement. This time, however, you are expected to enter a

The

is called a of

principal and interest.

name which you enter is stored in the variable N$.

ofa"string

"character

variable."

string."

The name that you type, for

Line60prints the message Line

65 prints the name stored

amount Line70skips a line (PRINTs a blank line). Line

A

In some cases the string may consist entirely considered a string as well as a numerical constant.

A following are all valid examples

In line numeric variable, the computer would continue to ask for data until a numeric constant was entered.

of

the investment.

80 transfers control

string

is any sequenceofkeyboard characters, for example

SMITH

JOHN

1023 N.

1982 MACROCORP MARCH $120.95

valid

N$, A3$,

MAIN

12, 1984

string

variable

DA$,

40,

it is essential that the variablebea string variable.Ifyou tried to use a

"TOTAL

back

to line 10.

STREET

is any numeric variable followed by a dollar sign ($). The

AD$,

ST$

FOR."

in

N$ followedbythe word IS, the symbol $, and the

of

digits (e.g. 1982), but it can still be

of

string variables:

of

The assignment statement.Itis possible to use assignment statements with string variables and constants statement:

assigns the string assignment statement, it is necessary to enclose the string

Each string variable assigned to string variables exceeds 256, you must set aside additional space. This is

done with the the program:

This particular instruction allocates space for

more than

When the Computer is turned

just

11Z11Z1

A$

5

CLEAR

300

the name to the string variable N$ was made with the

as with numeric variables and constants. For example, the following

=

"RADIO

RADIO

CLEAR

can

statement.

SHACK"

SHACK

hold up to 256 characters.Ifthe total numberofcharacters

to the string variable A$. When using an

in

quotes, as shown above.

For

example, the following line couldbeadded to

31Z11Z1

300

characters.Ifyou attempt to store

charactersinN$,

an error will result and the program will terminate.

on,

space for 256 characters is allocated automatically.

40

INPUT

If

you require more, then the CLEAR statement must be used. Since itisunlikely a name will be longer than 256 characters, the above program should not need the CLEAR statement.

If,

on the other hand, your program had twenty string variables, each of which is used

to

hold a name, then the maximum of 256 would probably be exceeded. In this case,

the CLEAR statement would be needed.

Experiment

Clear working memory with the NEW command and type the following program from the keyboard:

1121

INPUT

2121

R=R /

3121

INPUT

ill2l

INPUT

5121 8121 7121 8121 9121

When you execute this program, you will be prompted for the interest rate, the

amount

12

should be entered, not .12. Hereisan example of the execution of the program.

INTEREST

AMOUNT

NUMBER

MONTHLY

=

N

I

=

MP MP

PRINT

of

the loan and the lengthinyearsofthe loan. If the interest rateis12%

#8

"INTEREST

1121121

"AMOUNT "NUMBER

12

R /

= = A /

OF OF

PAYMENT

T

*

12

( 1

-

MP

"MONTHLY

RATE

LOAN?30000

YEARS

Mortgage Payment Calculation

(

121

1121121

A

) " ;

R

T

$"

j

MP

( 1

(0

RATE

OF

LOAN

OF

YEARS";

I)~(-N»

+

PAYMENT

-100)?

?

25

IS

$

-

II

;

/ I

IS

12

315.967242659281

then

Line10allows the interest rate to be entered and stores it in variable Line 20 converts the interest rate to a decimal value.

It

is

importanttonote that the equals symbol

the value computed on the right side to the variable on the left side."

is

mean the right side assignment statement:

R = R

means to compute the right side, R / 100, and then store the result backinR. Line 30 allows the amount of the loan to be entered and stored in numeric variable

Remember that numeric values are entered without a comma.

/100

equaltothe left side as in an algebraic equation. Thus the

41

(=)

in

a BASIC program means "assign

R.

It

does not

A.

Line40allows the lengthofthe loan (in years)tobe entered and storedinvariable T.

50 computes the numberofpayment periods (months) of the loan and stores the

Line value in variable

N. Line 60 computes the interest rate per month and stores it in variable Lines 70 • 80 compute the monthly payment. The computation

to

rather than one, Recall that the equals symbol

to

side then stored in MP.

Line Run the program several times with your own data. Have you ever wondered what

effect a change the program and vary the interest rate while keeping the other variables constant.

the variable on the left side. In line 80 the value

90 prints the amount of the monthly payment.

Experiment

avoid having a long, complicated expression in a single line.

(=)

meanstoassign the value computed on the right

of

AlMP

in

the"

interest rate would have on your mortgage payment? Just run

#9

Calculation

of

Total Amount

1.

was

done in two lines

is computed and

and

Loan Balance

In additiontocalculating the monthly mortgage payment,asin

to

you might wish multiplying the numberofpay periods N by the monthly payment MP. Type in lines 100

and 110asfollows:

100

110

compute the total amount you havetopay. Thisisdone

TA

= N *

PRINT

MP

"TOTAL

AMOUNT

PAID

IS

the last experiment,

$";

TA

by

Another calculation that can be made is the determinationofthe loan balance or

of

outstanding principal, after a certain number

120

INPUT

"CURRENT

YEAR

payments. Enter the following lines:

OF

LOAN"; Y

130 M = 12 * Y

140

B = (1 - (1 +

150 B =

MP

* B

160 PRINT "PRINCIPAL

Hereisa listing of the the complete program:

10

INPUT

20

R

INPUT

30

40

INPUT"NUMBER 50 N 60

I

70

MP 80

MP 80 PRINT 100

TA

110 PRINT

120

INPUT 130

M

"INTEREST

R / 100

=

"AMOUNT

12 * T

=

R / 12

=

(1

= =

-

A /

"MONTHLY

= N *

"TOTAL "CURRENT

= 12 * Y

MP MP

OF

(1

+

AMOUNT

l)h(M-N»

REMAINING

RATE

OF

LOAN";

YEARS";

I)h(_N))

PAYMENT

YEAR

OF

(0

PAID

/ I

IS

100)

-

A T

/ I

$"

IS

LOAN";

;

$";

" ;

MP

Y

B

R

TA

42

140

B =

(1

-

(1

+

I)~(M-N»

150

B =

MP

* B

180

PRINT

Here is an exampleofthe execution of this program:

"PRINCIPAL

REMAINING

/ I

IS

$";

B

INTEREST

AMOUNT

NUMBER MONTHLY TOTAL

CURRENT

PRINCIPAL

This example would be typicalofan

80% mortgage

The discouraging result

over the the principal remaining unpaid after 10

toward the original amount borrowed.

30 years

years you have paid

$71,200-$66,883.23=$4,316.77

RATE OF OF

PAYMENT

AMOUNT

YEAR

at

12.5% over 30 years. The amount of the loan would be $ 71,200. is

(0

-100)7

LOAN

YEARS7

REMAINING

$ 273,559.51.

?

71200

30

IS

$

PAID

OF

of

IS

LOAN?

running this exampleisthat the total you will havetopay

By

12.S

759.88752679191

$

273559.50964509

10

18

S

66883.232623196

$ 89,000 home purchased with a conventional

entering a current year of 10, you can see that

10

years is still $ 66,883.23. This means that in

What you have learned:

In this lesson, the use of string and numeric variables has been illustrated. Arithmetic

in

expressions have been used

INPUT statement was found

Computer.

the calculation of interest and mortgage rates. The

to

be a very convenient method of entering data into the

43

Lesson

It

is often necessarytowrite programs that will do one taskifa conditionistrue and another if the condition why this concept

#4

is

Sales Commissions

is

false. This is called branching. In this lesson you will learn

important and how to implement branching in your programs.

Experiment

A salesman is to receive a flat rate commission of the total salesisover $2000, thenhewill receive an additional

$2000.

over The formulas areasfollows:

Commission

Commission = .15 * sales + .20 * (sales - 2000)

Clear memory with the NEW command and type the following program:

1121

INPUT

ZI2I

CM=ST 3121IFST 4121

PRINT

Execute this program. The program begins by asking you to enter the amount of sales. Type:

1121121121

to compute the commission on one thousand dollars sales. Note that a dollar sign is not entered. The computer will respond with the message

COMMISSION

indicating a commission of $150.

~

#1

= .15 * sales

"AMOUNT

>

Sales Commissions

if

OF

*

.15

2121121121

THEN

"COMMISSION

IS

15121

15%

of his total sales. However,

sales are less than 2000

if

SALES";

ST

CM=CM+.20

IS";CM

20%

of the amount

sales are over 2000

* (ST -

2121121121)

if

Since the sales were less than RUN the program again and this time when you are askedtoenter the amount of

sales, type:

3121121121

to

compute the commission on three thousand dollars sales. The computer will respond

with the message:

~

COMMISSION

indicating a commission of $650. Since the sales exceed $2000, the commission will

15%

be Try running the program using your own sales data and confIrm that the program

computes the commission properly.

of $3000 plus 20%of$1000 (the amount exceeding $2000).

$2000, the commission is a straight fIfteen percent.

IS

85121

45

How the Sales Commissions Program Works

20

.--

__

'--_--,

COMPUTE 15%

COMMISSION

AMOUNT

OF SALES?

COMPUTE

ADDITIONAL

COMMISSION

COMMISSION IS

END

Figure

4-1.

FlowchartofSales

Commission

Program

When you execute the program, you will be prompted for the total sales. The commission then will

ut

Line Line

allows you to enter the total sales, which is stored in the variable ST.

28

computes the flat rate sales commission and stores it in the variable eM.

Line38contains a new statement, the

be computed according to the above scheme and printed.

IFITHEN

statement.Ascan be seen from the

flow chart in figure 4-1, the program must'branchafter line 20.

If

the sales exceed $2000,anadditional computation must be performed. However, if

this is not the case, then the sales commission is already calculated in line 20 and no

additional computation is required.

46

To accomplish this, the program must be able to test whether or not sales (ST) is greater than IFITHEN statement.

The

inequ~lity

ST>

$2000, and branch accordingly. This can be done with the useofthe

2000·

appearing in line 30 (between IF and THEN) is called a is false, then the next statement to be executed is in line 40. On the other hand,

is

condition

CM

will be executed before control passes on to line 40. In other words,iftotal sales are not greater than sales are greater than original flat rate commission.

The general format of the IF/THEN statement is

true, then the statement following THEN:

= CM + .20 * (ST - 2000)

2000, no additional calculations are performed in line 30. But,iftotal

2000, the additional commissioniscalculated and added to the

"condition."

If

this condition

if

the

IF "condition" THEN "statement"

where "statement" is executed only when "condition"istrue. In either case, the next line executed is the one following the IFITHEN statement.

of

The condition is usually the comparison numeric expressions are compared with the use

..

>"

in line 30 is the relational operator.

Here is a table

numeric operator meaning

of

numeric relational operators:

two numeric or string expressions. Two

of

a relational operator. In this case,

> greater than

< less than < > or > < not equal to

> = or => greater than or equal to

<= or =< less than or equal to

Assuming the variable A has the value given below.

condition A>l

A < - 1 A

< > 1

A

>=

2

<=

A

Here are some more examples

55 IF A 65 IF 5.6 75 IF CD/AC

0

of

valid IF/THEN statements

* B - C < D THEN A = B

< >

AB-4.6

< > 1 THEN CD = AC

THEN STOP

2, the logical values

logical value true

false true true false

47

of

some conditions

are

Each condition can contain only one relational operator. Thus the following condition is not allowed:

A<>B<>C

It

should be clear that IF/THEN is a very powerful statement because it allows the program to carry out different tasks and functions, depending upon the value or values of

numeric expressions.

Experiment

One unsatisfactory aspectofthe Sales Commision program is that the value printed for

the commission does not directly indicate dollars in the customary fashion. Run the program and enter the value 1763.89 for the total sales. You will see that

264.5835 is printed out for the amountofthe commission. The outputofthe program is a decimal number that sometimes contains more than two digits to the rightofthe decimal point.

It

would be much neaterifthe commission were printed to the nearest cent each time.

One wayofaccomplishing this is to use a different print statement. Insteadofusing PRINT, the PRINTUSING statement can be used to format the output.

Make the following changes to the program: Change line 40 as follows:

40

PRINT

and add a new line 50

50

PRINTUSING

Line 40 will display the message

COMMISSION

and line 50 will print the valueofthe commission. Nowifyou execute this revised program you will see that the commission is printed, as desired, rounded to the nearest cent.

#2

Printing Dollars and Cents

"COMMISSION

"####.##";

IS

";

CM

For example, run the program and enter 1763.89 as the sales amount. This time the commission amount prints as 264.58.

The string enclosed in quotes,

####.##

is called a format specifier, and it indicates how a number is to be printed.

Since twoofthe # symbols appear to the rightofthe decimal point, exactly two

digits will be printed to the rightofthe decimal point.

of

four digits to the left will be printed. (Fewer than four digits to the leftofthe

decimal point maybeprinted, depending on the sizeofthe number.)

48

By

the same token, a maximum

Since there are six # symbols and one decimal point specified, a totalofseven

of

columns will be used for the printing "right justified" in this seven column field, meaning that there may be some blanks in the left most columns, but not in the right-most.

the number. The number will be printed

Instead.ofusing a constant string, such as string variable for the format specifier. For example, the program can be changed as follows

as

A$

=

"####,##"

S0 PRINTUSING A$;

This will give the same outputasbefore. Again, the value printed for the commission will be rounded to the nearest string or a string variable, is always followed by a semicolon.

For some more examples, suppose CM this is printed out with line 50 above. The following table gives the output for various format specifiers

format specifler

A$ = A$ =

A$

Experiment

There are other possibilities for format specifiers. Change line 45 in the program so

that it is:

A$ =

=

"####.##" "####.#" "#####.###"

"####.#####"

#3

eM

cent. Note that the format specifier, whether it is a

Dollar Signs

"####.##",

it is permissibletouse a

= 1416.3812 (actual value as computed) and

output

1416.38

1416.4

1416.381

1416.38120

as

A$

=

"$######,##"

Now run the program and input a varietyofvalues for the sales. In each case there will be a dollar sign will be some blanks between the

Now change line 45 so that it

as

A$

Run the program with a sales amountof1111.Asyou can see, the $isnow printed

just to the left

numeric field specifier instructs the computer to print a dollar sign immediately to the

of

the leading digit.

left

Experiment

Many times, payroll checks are printed with asterisks padding the leftmost columns the field.

Change line

as

45

A$

($) printed to the left

$ and the left most digit

is:

=

"$$######,##"

of

the number $166.65. The useoftwo dollar signs to the leftofthe

#4

in the previous program to:

=

"**$######,##"

Checks

of

the field (9 column). In many cases there

of

the number.

of

49

Run the program with a sales amount of 1111. In this case you can see that in the

of

output

the commission

..........

the unused positions are, indeed, padded with the Large dollar amounts are usually printed with commas. Try changing line

45

Run the program with a sales amountof123456. In the output of the commission,

***$42,809.60

the digits are now separated with a comma to make the readingofthe number easier.

If

your number requires more columns than you have specified, for example printing

34.56 with

be

printedtothe left of the numbertoindicate the field overflow.

Experiment

Change the sales commission program so that it is computed accordingtothe following scheme:

if

The program must now make two different computations depending upon the total sales.

$166.65

"*,,

symbol.

A$

=

"**$###,###.##"

"#.###",

sales are $2000 or under, commission is sales are over $2000, commission is 20%ofsales

the number willbeprinted anyway, but the symbol

#5

Sales Commission Revisited

15%

of sales

45

to

"%"

will

The program is illustrated with the flow chart in figure 4-2. The branching can accomplished with the useofa variationofthe IF/THEN statement, called the

IF/THENIELSE statement.

be

50

~-

AMOUNT

OF SALES?

20

COMPUTE

COMMISSION

30,40,50

YES

15%

END

NO

COMPUTE 20%

COMMISSION

IS

Figure 4-2. Flowchart of Experiment 5

Modify the program by deleting line 20 and replacing line

3121

IF

ST

<-

2121121121

-

.2121*ST

Since this line requires more than 40 columns, it will not fit on a single lineofthe display of your Model 100, but will overflow

to

255

may contain up display.

characters, in which case it will extend over several linesofthe

THEN

CM-.15

to

the next line. A line in your program

51

30:

*

ST

ELSE

CM

A lineisterminated only when you press

to

List the program

10

INPUT

20

IF

40

PRINT

45

A$

50

PRINTUSING

Execute the program. When prompted for the amount

computed as Run the program again and enter a sales

computed The IF/THEN/ELSE statement is used to execute one

depending upon the logical value

If

sales are less than or equalto2000, the commissioniscalculated as and control passes following ELSE is executed instead, so that the commission is calculated as 20% of

sales and again control passes

as

confirm that it

"AMOUNT

ST

<=

2000

OF THEN

"COMMISSION

=

"**$###,###.##"

A$

;

of

$150.00, which is a straight 15%.

$600.00 which is a straight 20%.

of

to

line 40. However,ifsales are over 2000, then the statement

to

line 40.

(ENTER)

is:

SALES";

CM

and notatthe endofa display line.

ST

=

.15

*

ST

ELSE

CM

IS";

CM

sales, enter 1000. The commission will be

of

3000. This time the commission will be

of

two different statements

the condition.

15%ofsales

=

.20

*

ST

The general format of the IF/THEN/ELSE statement

IF

"condition" THEN "statement

"statement

"condition" is false

if

In either case, control passes

can be any valid BASIC statements. Here are some more valid examples

IFITHEN/ELSE statement:

100 IF A = 0 THEN A = B + 1 ELSE A =

200 IF A + B < 100 THEN A = B ELSE A = 0

Experiment

]"

is executedjf "condition"istrue, but "statement2"is executed

to

the next line in the program. The statements executed

#6

Computing Commissions for

]"

ELSE "statement

is:

B-1

2"

of

the

Several Salesmen

The Commission Sales program,asit currently exists, will compute the commission for one salesman and terminate. To compute the commissions for several salesmen, it must be modified.

List the programtoconfirm that it still looks like this:

10

INPUT

20

IF

CM

40 PRINT

45

A$

50

PRINTUSING

"AMOUNT

ST

<=

2000

=

.20

*

"COMMISSION

=

H**$###,###.##"

ST

A$

OF

THEN

;

CM

SALES";

CM

=

IS";

ST

.15

*

ST

ELSE

"

52

Line10will be changedsothat the nameofthe salesman can be entered along with the sales amount.

10

INPUT

The name will be placed in the string variableN$and the sales amount in the numeric variable ST. Line 20 will correctly calculate the commission, but line 40 must be altered so that the name

40

PRINT

If

the name entered is SMITH, then line 40 will print

"NAME,

SALES"; N$,

is

printed. Change line 40

"COMMISSION

FOR

";

ST

to:

N$;"

IS

";

COMMISSION

and

line 50 will print the amountofthe commission after the word IS.

Here is a listing of the program after the changes have been made:

10

INPUT

20

IF

ST

CM

=

40 PRINT

45

A$

=

50

PRINTUSING ASi

If this program were executed, it would compute the commissionofa single salesman and execution would terminate. commission, it must branch back a

GOTO

Now the programiscomplete:

statement after line 50. Type in a new line:

G0

GOTO

10

INPUT

20

IF

ST

CM

=

40 PRINT

45

A$

=

50

PRINTUSING A$i

G0

GOTO

FOR

SMITH

"NAME,

(=

.20

SALES"; N$,

2000

*

THEN

ST

"COMMISSION

"**$###,###.##"

If

10

"NAME,

<=

.20

SALES" i NS,

2000

*

ST

"COMMISSION

"**$###,###.##"

10

IS

CM

=

FOR

"i

CM

the programisto

to

line

10.

This can be accomplished with the use

THEN

CM

=

FOR"

CM

ST

.15

*

ST

ELSE

N$i"

IS

";

compute more than one sales

ST

.15

*

ST

ELSE

iNS;"

IS

";

of

This program illustrates a concept in programming called a block of statements are repeated several or perhaps many times

program above, the entire program is repeated, each time with a different salesman

It

and sales total.

it

means Try running the program and entering several names and sales amounts. Be sure to

press

will not terminate and must be manually terminated by pressing

~

should be noted that the program is an "infinite loop," which

when you wishtoterminate execution.

53

"looping."

in

This means that

a program. In the

(BREAK).

Experiment

#7

How to Escape From

an

Infinite

Loop

It is easy to add some statements so that programs that contain infinite loops will terminate upon request.

be

In the Sales Commission program, for example, the sales total will never But you can modify the program so that it terminates whenever a negative value for sales is entered.

new

Type the

15

The

STOP

~.

Run the program. When prompted to do so, enter a dummy name (such as END) and a negative sales

amount (such as computing any commission.

The dummy name was necessary because the INPUT statement in Line 10 requires you to enter two input quantities. Since a negative sales amount terminates execution, the name you enter will not be used.

You can have more than one program need not have any STOP statements in it at all.

line:

IF

ST

< 0

THEN

statement, terminates execution and has the same effect as pressing

The program will terminateifST

-1).

Note that the program terminates immediately without

STOP

(ENTER)

is negative, but continueifit is not.

statement in your program.Ofcourse your

negative.

Experiment

#8

Individual Commissions for the

Salesmen

The Sales Commission program calculates every salesman's commission using the

same

rate. Nowwewill modify the program so that each salesman has his

commission rate. Here is a listofsalesmen and their commission rates:

Name ADAMS

JONES

LEE

SMITH

VINSON

of

When any the corresponding rate before the commission can

changes to the program: Retype line 20 as follows

20

the above names is entered, the program must lookinthe table to find

READ

NU

t

CR

Rate

15% 16% 18% 20% 14%

be

calculated. Make the following

own

S4

and add lines 24, 26 and

24

IF

Nl$

28

CM=ST

28

RESTORE

Delete line 30. Now the only remaining change

line:

70

DATA

ADAMS,.15,JONES,.18,LEE,.18,SMITH,.20,

<>

28

N$

THEN

*

CR

GOTO

is

to add the table to the program. Type the following

VINSON,.14

List the programtoconfirm that you have:

10

INPUT

15

IF

20

READ

24

IF

28

CM=CR*ST

28

RESTORE 40 PRINT 45

A$ 50 PRINTUSING A$; 80

GOTO 70

DATA

"NAME,

ST

< 0

Nl$,

Nl$

<>

"COMMISSION

=

"**$###,###.##"

SALES"; N$,

THEN

STOP

CR

N$

THEN

GOTO

FOR

CM

10

ADAMS,.15,JONES,.18,LEE,.18,SMITH,.20,

VINSONt.14

";

20

ST

N$;"

IS

";

Run this program. Be

sure to enter one of the five names listedinthe table. The program will compute

in

any

and print the commission for that salesman. Continue to input names their corresponding sales totals. To end the program enter a dummy name and negative value for the sales amount.

20 reads the first name (ADAMS) listed in the DATA statementinline 70 and

Line

It

places it in the string variable NI$. it in the variable CR.

Line 24 compares the name in N$, which was entered in line 10, they are different, the program jumps back to line 20 which then reads the next name

in

and commission rate way until a match is found. When this happens, commission rate for the salesman.

Line 26 computes the commission for the salesman.

is

the

Line 28 will go back to the first item in the data list. Therefore the next time a READ statement

Without RESTORE, the reading of the time before. from

the beginning each time.

The remainder of the program is the sameasbefore, with the exception of line 70. Line 70 contains the DATA statement from which the names and rates are read. This

RESTORE

is

executed,itwill use the first iteminthe DATA list.

If

the names are entered in an arbitrary order, the data list must be read

the DATA statement. The program continues looping in this

statement. When this statementisexecuted, the computer

reads the first commission rate (.15)

to

that in NI$.

CR

will contain the correct

data would continue where it left off from the

order and

and

places

If

55

statement can be placed anywhere in the program, butitis at the beginning or the end of the program.

is

What would happen if a name Run the program and enter the name CARTER and a sales amount

program continues reading names program terminates and displays the error message:

?OD

ERROR

indicating that an OUT OF DATA error occurredinline 20. The program triedtoread past the last name and rate in the list.

Additional names and rates can be added

statement. The computer treats multiple DATA statements

IN

entered, whichisnot in our list?

in

the DATA list until it runs out of data. The

20

to

line 70 or placedinanother DATA

traditional to place it either

of

1000. The

as

one continuous list.

What you have learned:

In this lesson you have learned how a program can be madetoBRANCH and accomplish different tasks depending upon the value of a variable or expression. This

by

can be done to

format the output so that it was presentedina more reasonable fashion than would be the case with just the PRINT statement. You saw to terminate execution under program control. You also learned that the READ/DATA statements often provide a convenient method of inputing data especially frequently referenced data like tables and lists.

using the IFffHEN statement. The PRINTUSING statement was used

howtouse the STOP statement

to

the program,

56

Lesson

Your Model 100 has a numberofstring functions which allow you to manipulate

string constants and string variables in various ways.

#5

Day, Time and Date

In this lesson you will learn how to use some special string functions that

the day, time and date. Also, other string functions will be used to extract information

from string constants and string variables and to output character data.

Experiment

DAY$ is a string function which returns the dayofthe week.Ifyou type:

PRINT

you will see that the first three lettersofthe present day are displayed. For example, today happens to be Thursday, the Computer will display

DAY$

#1

What Day is it?

wrnID

"return"

Thu

Note: You must initialize the day sometime prior to using the DAY$ function. Once initialized, the day will be automatically updated.

If

you have not already initialized the day, this can be done by entering the following

command:

DAY$ =

where

"xxx"

Monday, enter

DAY$

While the DAY$ function returns the first three lettersofthe dayofthe week, it is often desirable to print the full nameofthe day (e.g. Thursday, not Thu).

"xxx"

are the first three lettersofthe current day. For example,iftoday is

=

II

M

ON"

CEBIEID

if

The following program, which we'll call DAY, accomplishes this. Refer to Figure 5-1

for a flowchartofthe program. Clear working memory with the NEW command and type the following program in

from the keyboard.

10

READ

20

IF

30

GOTO

40

PRINT

50

DATA

60

DATA

Execute this program. The program will output the dayofthe week. Hereisan exampleofthe output:

TODAY

0$

LEFT$(D$,3)-

10

"TODAY Sunday, Thursday,

IS

Thursday

DAY$GOTO

IS

";

Monday,

Friday,

0$

Tuesday,

57

40

Wednesday

Saturday

How program

DA

10

Y works:

READ DAY

ASSIGN TO

D$

TODAY IS

END

Figure 5-1. Flowchart of Program DAY

Line

18

A string from line 60 or 70 is read and assigned to the string variable The first time line 10 is executed, the string Sunday will be assignedto0$, second time line 10 is executed, Monday will

Line

28

The IF / THEN statement compares DAY$ with the first three characters stored

in

0$.

DAY$ contains the first three charactersofthe current day (SUN,

MON, etc.). LEFT$(D$,3) returns the three leftmost letters

If

a match occurs, the program jumpstoline

Note that the IF statement does not contain the keyword THEN. optional

Line

be

in

an IF statement when it is followedbya GOTO statement.

38

The GOTO statement transfers control back to line10where the next day will

read from the data list.

Line 48 The PRINT statement displays the message

day

of

the week.

be

assigned to

40,

otherwise line 30 is executed next.

"TODAY

0$,

etc.

of

the string stored in

The

keyword is

IS"

followed by the

0$.

the

0$.

58

Lines 58 • 68 These DATA statements contain the listofthe days of

the

week.

Lowercase letters must be used for the second and third characters to correctly match

of

DAY$, which stores the first three characters of each day

the week (an uppercase

and two lowercase letters). This program uses two string functions,

of

the first three letters

the day of the week.

DAY$and LEFT$. Recall thatDAY$

The function LEFT$(D$,3) returns the first three characters of the string stored

D$

For example, if

has Thursday assigned to it, then

PRINT LEFT$(D$,3)

would display

Thu

of

The number 3 indicates the number D$

contains Thursday, then

Command PRINT LEFT$(D$,1)

PRINT LEFT$(D$,2)

PRINT LEFT$(D$,5)

characters to be returned. Again assuming that

Displays

as

T Th

Thurs

etc.

is

LEFT$ characters

a string functionoftwo arguments, the string (D$) and the number of

to

be returned. The first argument need not be a string variable, it can also

be a string constant. For example,

PRINT

would display

Mod

LEFTS(

as:

"Model

100"

,3)

returns

in

D$.

When a string constantisusedasthe argument, it must be enclosedinquotation marks.

DA

The last character in the name of both functions, LEFT$ and

($)

because the quantity returned,inboth cases,isa string.

Experiment

Program DAYisto centered in the line with an equal number

#2

Centering the Day

be changed so that the output will consistofthe day of the week,

of

asterisks (*) printed on both sides.

Y$,isa dollar sign

Make the following changes:

40

Retype line

1I0 L = LEN·(

as:

OS)

and type four new lines:

5 CLEAR

1I1i

AS =

~G

OS

LIB

PRINT

100

STRINGS(

= AS +

OS

(1I0 -

+ AS

L)/2,

59

u*U)

Now list the program to confirm that it is:

5

CLEAR

10

READ

20

IF

30

GOTO

40

L =

44

A$

48

0$

48

PRINT

50

DATA

80

DATA

Execute the programbyentering the RUN command.Ifthe current dayisThursday,

the following will be output:

100

D$

LEFT$(D$,3)

10

LEN(O$)

=

STRING$(

=

A$

+

D$

SundaY,

Thursday,

=

DAY$

(40

+

A$

Monday,

Friday,

-

L)/2,

THEN

Tuesday,

Saturday

GOTO

"*")

40

Wednesday

****************Thursday****************

If

the current dayisFriday, then the output will appear

*****************Friday************~~***

In

each case, the wordiscentered in the line and an equal number of asterisks are

printed on both sides to fill the line.

16

characters, then The function

constant. For example if value 6, and LEN("Friday") also returns a

Since

the

value returned by the function LENisan attachedtothe function name. In line 40, the number of characters of the string stored in0$is

a<;signed

asterisks are printed on both sides so that39columns are used.

LEN

returns the numberofcharacters in a string variable or string

0$

contains Friday, then the function LEN(O$) returns the

to

L.

If

the current dayisFriday, then L has 6 assigned to

If

the current dayisTuesday, which has 7

6.

as:

integer, thereisno dollar sign ($)

it.

60

Since each line has 40 print columns, the number of asterisks to be printed on each side

of

the day

is

(40 - L)/2.

For example,

if

the current day is Friday, 17 asterisks must be printed before and after

the word Friday. In line 44, the function STRING$ is used to construct a string of asterisks

if

correct length and assign it to the variable A$. Again,

(40 -

and STRING$( (40 - L)/2,

L)12=17

"*")

will be a string of17asterisks.Ifthe current day

L has the value 6, then

of

the

Tuesday, then L = 7 and

(40 - L)/2

This value will be truncated to

= 16.5

16

in the STRING$ function so thatA$will have

length 16.

gener~

The

STRING$(r,

formofthe STRING$ function

"x")

is

which constructs a string consisting of r repetitions of the character x. The argument r can be a numeric constant, variable or expression. For example, if

J=3

and

M=2

Command PRINT STRING$(5,

PRINT STRING$(J,

"#")

"X")

PRINT STRING$(J-M,"&")

Displays

#####

XXX

&

as

is

Line 46 illustrates the concatenation operator +. The strings A$,

joined together to form a new string which is then assigned concatenation operator can

be

used with string constants or string variables. For

to

the variable

example:

A$="RADIO"+"SHACK" concatenates the two strings

"RADIO"

and

"SHACK"

together to form a new string

"RADIO SHACK" and assigns Note that

Thus the old value which was assigned to

ittothe string variable A$.

in

line 46,

0$

appears both on the left and the right side of the equal sign.

0$isreplaced by the new string, which

printed in line 48.

D$

andA$are

0$.

The

is

61

Experiment

Another useful featureofyour Model 100 Computeristhe string function TIME$, which returns the time

hh:mm:ss

#3

What time

as

a stringofthe form

is

it?

For example, if the time

PRINT TIME$

would print

13:05:00

The first two digits indicate the hour(lPM), the second two digits the minutes;

minutes after 1), and the last two digits the seconds.

The clock is a 24 hour clock,

indicating midnight. Note: The time must be initialized prior to using the TIME$ function. Once set,

keep the correct time just like a clock. you may do so by entering the following command:

TIME$

where hhisthe hour, mm the minute, and ss the seconds. The hourisin 24 hour format,

TIME$

The following program will convert the string returnedbyTIME$, for example

14:18:00, to the customary format, 2:18 PM.

Clear the previous program from memory with the NEW command and then type the following program:

= "hh:mm:ss"

so

that 3 PMishour 15. For example, if the current time is 3:05 PM, type

=

is

exactly 1:05 PM, then the following command:

"15:05:00"

so

the hours will range from 00to23, with 00

If

you have not already initialized the time,

(ENTER)

(5

it

will

10

HH$

=

LEFT$(TIME$,2)

20

HH=VAL<

30

IF

HH>=

40

IF

HH

50

HH$

= STR$(HH)

60

MMS=MID$(TIME$,4,2)

70

T$

=

80 PRINT

After the program has been entered, execute it with the RUN command. An example

of the output is

THE

TIME

LineHtThe first two characters in TIME$ are assigned to the string variable HH$. These two characters designate the hour. For example, if it

contain the two characters 13. Since LEFT$ returns a string, these two characters form

a string even though they are numerical digits. Thus they cannot be assigned to a numeric variable.

> 12

HH$

"THE

IS

HH$)

12

+

1:05

THEN THEN

":"

TIME

PM

A$

= "

HH=HH

+

MM$+AS

IS";

62

T$

PM"

- 12

ELSE

A$

= "

AM"

is

1:05 PM, then HH$ will

Line 28 The string assigned to HH$ is convertedtoa numerical valuebythe

VAL

function. This numerical valueisassignedtothe numeric variable HH. Using the

13

previous example, HH would have the number

to

function, it would not be possible

make this assignment.

assignedtoit. Without the VAL

38 This statement determines whether it

Line

to

string value

A$. The value stored in HHiscomparedtothe numeric constant

is

AMorPM

and assigns an appropriate

12.

Only a numeric variable can be usedinthis way. The useofHH$ would have

was

produced an error and it was for this reason that the string stored in HH$ to

a numeric constant and assignedtothe numeric variable HH.

48

Line example, hour previous line, the variable must

is

Line 58 This line uses the STR$ function

back

The hour value is converted from a 24 hour format to a12hour format. For

13

would be converted correctlyto1 (PM). In this line,aswell in the

be

a numeric variable. The statement:

HH$

= HH$ -

12

illegal and would produce an error.

to

convert the numeric value storedinHH

to

a string whichisthen assigned backtothe string variable HH$. This will

changed

be

concatenated later with another string. In order todothis, a string variable must be

used.

Line 68 This line uses the MID$ function

to

read the two minutes digits from TIME$ and stores this two-character string in the string variable MM$. Note that the minutes are the 4th and 5th characters in the string:

13:05:00

MID$(TIME$,4,2) returns two characters starting with the 4th from the left.

Line 78 In this line, the string to

variables HH$ (hour), MM$ (minutes), and

be

printedisconcatenated together from the

A$

(AM or PM). A colonisinserted

between the hour and minutes.

Line

88

The message

Here are some examples of TIME$ and the resulting output

TIME$ 10:15:12

17:08:55 03:18:43

"THE

TIME

IS"isdisplayed followed by the time.

OUTPUT

THE TIME

IS THE TIMEIS5:08 PM THE TIME

IS

10:15 3:18

AM

of

the program:

Note that a leading zero is not printed for the hour. This leading zeroislost when the VAL function

is

applied.

The function VAL converts a string constant or variabletoa numeric value. The following examples illustrate this function:

string

123ABBA

2.3CA987

567.4

The leftmost characters, up are converted to a number. This function

VAL

123

2.3

567.4 to

the first character which cannot be partofa number,

is

useful when it is necessarytouse a

63

numeric string constant in a numeric expression. The number in string form must be converted to a numeric constant before it can be used in a numeric expression.

is

The STR$ function or variable to its string form. This

with another string

the inverseofthe VAL function.Itconverts a numeric constant

is

useful when you want to concatenate the number

as

was done in this program.

MID$(string,p,n) returns the sub-string

The

character. This is illustrated with the following examples:

string ABCDEFGH

JUNE 18, 1983 RADIO SHACK

Experiment

The program in Experiment 3 did not print the seconds even though they are returned by TIME$. The program will be changed so that the output will appear

THE

TIME

Make the following changes to the program: Type a new line:

65

55$

and change line 70 to

70

TS = SSS

List the program to confirm that it

#4

IS

=

RIGHT$(TIME$,Z)

HHS

+ " SECONDS"

p

5 10

7

Printing the Seconds

1:05

+

":"

PM

AND

+

MMS+AS

is:

of

length n starting with the p-th

n

3

2

5

28

MID$(string,p,n) EFG

19

SHACK

SECONDS

+ "

AND"

as:

+

10

HHS

=

LEFTS(TIMES,2)

20

HH

= VAL(HHS)

30

IF

HH

>=

12

THEN

40

IF

HH

>

12

THEN

50

HHS

=

STRS(HH)

60

MMS=MIDS(TIMES,4,2)

65

SSS

=

RIGHTS(TIMES,2)

70

TS =

+ " SECONDS"

80

PRINT "THE TIME

Execute this program. The output will depend on the time.

displayed:

THE

Line 65 The RIGHT$ functionisusedtoreturn the two rightmost characters stored in

TIME$. These characters are the seconds and are assigned to the string variable SS$. The RIGHT$ function is similar

TIME

HHS

IS

+

5:23

":"

AS

= "

PM"

ELSE

HH=HH

+

MMS+AS

IS";

If

TIME$ = 17:23:56, then the following will be

PM

AND

to

LEFT$, except that the digits are counted from the

TS

56

64

-

12

+ "

SECONDS

AS

AND"

= "

+

AM"

SSS

right instead of the leftofthe string.Ofcourse, the MID$ function could have been

65

used instead. Using MID$, line

65

SS$ =

It

is usually easiertouse

leftmost or rightmost

MID$(TIME$t7t2)

LEFf$

of

the string.

would appear

or RIGHT$ insteadofMID$ if the characters are the

as:

Experiment

The string function DATE$ returns the date in the form

mm/ddlyy

For example,

PRINT

will display

if

#5

What's the date?

the present date is October 23, 1983, then the command:

DATE$

10/23/83

Note:

The date must be initialized priortousing the DATE$ function. Once entered,

If

the date will be automatically updated.

maydoso by entering the following command:

you

=

DATE$

where

mm

yy the year. For example,

DATE$

Delete the previous program from memory with the NEW command. The following program will print the date in the usual form, (i.e., the name and the year.) For example:

DECEMBER

"mm/dd/yy"

is the numberofthe current month (e.g.03for March),ddis

if

todayisDecember 25, 1983, enter

=

"12/25/83"

25t

1983

you have not already initialized the date,

the day, and

of

the month, the day

Type the following program:

10

MM$

= LEFT$(DATE$t

20

MM=VAL<

30

READ

110

CT=CT

50

IF

CT

80

DD$

= MID$(DATE$,

70

YY$

= RIGHT$(DATE$,

80 PRI 90

100 110

RefertoFigure 5-2 for the flowchartofthis program. Execute the program. The output will be today's date in the usual format: month, day,

and year.

NTMM$;

DATA

DATA DATA

MM$)

MM$

+ 1

<

MM

THEN

"

JANUARY,

MAYt

JUNEt JULYt

OCTOBERt

";

FEBRUARY,

2)

GOTO

ll,

30

2)

DD$;",19";YY$

MARCHt

AUGUSTt

NOVEMBERt

65

DECEMBER

APRIL SEPTEMBER

How Program

"What's

the

10

20

30

40

date?"

Works

SETMM$

TO MONTH

CONVERT

MM$TO

NUMERIC MM

READ MONTH

FROM DATA

LIST

INCREMENT

COUNTER

NO

60

SETDD$

70

80

DAY

SETYV$

TO YEAR

TO

--0

Figure 5-2. Flowchart of Program "What's the date?"

66

Line18The left two charactersofDATE$ are stored in the string variable MM$. This is

the month. For example,ifthe monthisOCTOBER, then

"10"

assigned to it. Itisimportanttoremember that LEFT$ returns a string, not a

numeric constant.

MM$

will have the string

28 The string stored in

Line function. This must be done because it will

to

number Line 38

fIrst time, JANUARY is assignedtoMM$. Since the string originally stored in will no longer be needed, the string variable MM$isreused in this line.

Line the value 1 because the computer initializes all numeric variables to zero when the program is executed.

Line program will jump back to line Eventually, CT will equal MM. When this happens, assigned

into MM$, until the present month

loop (lines

Line by

the 4th and 5th characters of the string stored in DATE$.

Line that the year is given by the last two characters.

Line followedbya semicolon which means that no columns aretobe skipped.Itwas necessary printed immediately after the month.

another numeric constant in line 50.

The next month is read from the DATA statements and placed in MM$. The

48 This line increments a counter CT. After the first month is read, CT

58Ifthe counter CT is less than the numberofthe current month; then the

to

it and line 60 will be executed next. Thus, the months

30, 40 and 50).

68 The MID$ function is used to extract the day from DATE$. The day is given

78 The RIGHT$ functionisusedtoobtain the current year from DATE$. Recall

88

The date is printed in this line. Note that each item in the print list

to

print a blank space after the month, or otherwise the day would be

MM$isconvertedtoa numeric constantbythe VAL

be

necessary to compare the month

MM$

w~ll

30, where the next month is read from the data list.

MM$

will have the current month

are

read repeatedly

is

reached, and then the program jumps out of the

is

have

98 - 118 These DATA statements contain the months of the year which are read

Lines by the READ statement in line

30.

What you have learned:

In this lesson the three special string functions DAY$, TIME$, DATE$ and some of their uses have been illustrated. Various other string functions have been used extract information from string variables andtoprint out certain string quantities.

67

to

Lesson

In this lesson you will learn how to use the built-in Editorofthe Model 100sothat changes

Until now, you have been able following three ways:

I)

2)

3) While any change

they can be time consuming. For example, character

move one linetoanother location in the program, the old line must be deleted and the line retyped with a new line number.

to

An

existing lineischanged by retyping it.

An

existing lineisdeletedbyentering just the line number.

A new line is added by enteringitwith the appropriate line number.

in

#6

a BASIC program can be made quickly and easily.

a lineofyour program, the entire line must be retyped.Ifyou want·

Using the Editor

to

make changestoyour BASIC programsinthe

to

your program can be accomplished using these three procedures,

if

you only wanttochange a single

to

An easier and more efficient way to make changes

to

Editor. The Editor allows changes line. It also allows a line number

There are other convenient features examined in detail.

Experiment

Enter the following program from the keyboard exactlyasitisprinted here:

10

INPUT

20

READ

30 IF

00 PRINT

50

DATA

80

DATA

This program prompts you for a name.Ifoneofthe names in the DATA statements entered, (i.e. BETTY), the corresponding age (35) willbedisplayed. If the name entered is not found in the DATA statements,

is

how the programissupposedtowork).

that

A$,

A$

DAN, BETTY,

#1

Inserting a Character

~NAME";

AG

< >

N$

~AGE

IS",

32,

be made to a line without retyping the entire

to

be changed without retyping the line.

of

the Editoraswell. These features will be

N$

THEN

GOTO

A

RON,

35,

38,

RALPH,

of

this type istouse the built-in

20 LINDA, 02

29,

SKIP,

an

outofdata error will result (at least

3

is

69

Run the program. If you enter the name LINDA, the output will look like this:

i'M\ME?

AGE

Ok

1....

I~"3

I

NDf\

~~

II

Obviously, the programisnot working correctly. The correct ageis42, not 0. The problem

Line 40 should appear

This error could be corrected by retyping the lineasshown above. But instead, we'll use after A. Type the command

You will see the following displayed:

isinline 40. Variable A at the endofthis line should be changed to AG.

as

£10

PRINT

the

Editor to change the variable name to

ED

I T

(ENTER)

10

INPUT "NAME";

2~:J

I~EAD

30

IF

40

PRINT

S0

DATA

60

DATA

"AGE

1'~'S

'j

A$<>N$

"AGE

DAN, BETTY,

,·\G

THEN 32,

15",

IS",

35,

NS.

GOTO

A.

RON,

RALPH,

AG

AGbyinserting the single character G

20

38,

LINDA,

29.

424

SKIP,

3

The Computer enters the editor mode and the programisdisplayed. The cursorison

the

first character of the program. The symbol

at the end when

To insert the is

directly over the .... in line 40.

The cursor

of

(ENTER)

is

each lineisused to display the carriage return character thatisgenerated

is

pressed. The

"G"

after the variable A in line 40, the cursor must be movedsothat it

..,..

displayed after line 60isan end-or-file marker.

moved using the four Cursor Movement Keys in the upper right comer of the keyboard. The arrows indicate which way the cursor will be moved when the key

is

pressed.

70

Press the down arrow key three times. This should place the cursor on the 4 in line

40. The display should appear

I:~!

E~

l·:j

D

(-~i

~i~

.,

IF

A$~::>N%

PP I

i\~T

II

l,\(;;iE:

DATA DATA

DAN, BETTY,

,t;

(;~<{f

THEN

I

~:.~

32,

35.

as:

II

OJ

RON,

GO"f'O

l~

RALPH.

38,

LINDA,

29,

SKIP,

42~

3~

The cursor must now be moved to the right until itisover the last character (the

triangle) in line 40. move to the right until the key move the cursor to the desired position.

If

the right arrow keyispressed and held down; the cursor will

is

released. Using the right arrow keyinthis fashion,

If

you go too far, use the back arrow key to

back up to the correct position. Once the cursor

done simply by pressing notice that the letter G

is

correctly positioned, you are ready to insert

CID.

Do NOT press

is

displayed in the correct place and the carriage return

(ENTER)

after

the

letter G. This is

CID

is

pressed. You will

character moves one column to the right. At this point, the display should appear

INPUT "NAME";

j~E:tlD

IF

.<+~~

PF~INT

DATA

1",

:;;

~

A$<>NS

"l\(::iE:

DAN,

BETTY,

,1\6

When the Editor is used, the systemisalways in the if

a keyboard characteristyped, this character will be inserted in the line where the

cursor was placed. Characters

THEN

I~:)",

32,

35,

to

Ns4

GOTO

RON,

20

It:;G~

38,

RALPH,

LINDA,

29,

SKIP,

42~

"insert"

mode. This means that

the rightofthe cursor move over to make room for

the inserted character. You must remember to use the arrow keys

space bar or Now that

CENllID.

"G"

has been inserted, you must exit from the Editor before you can

to

move about on the display, and not the

execute the program. To exit from the Editor:

as:

PRESS

THE

ESCAPE

PRESS (lID once

KEY

(ESC)

TWICE

71

or

After this is done, you will be back in BASIC with the updated program. Listitto verify that it

10

20

30

l10 50 80

Note that line 40 contains the correct variable AG. Execute the program. Hereisan exampleofthe

is:

INPUT

READ

IF

AS PRINT DATA DATA

output:

"NAME";

AS,

AG

< >

"AGE

DAN,

BETTY,

NS

32,

THEN

IS",

35,

N$

AG

RON,

RALPH,

GOTO

38,

20

LINDA,

2S,

SKIP,

l12

3

NAME? AGE

Ok

LINDA

IS

42

II

Run the program several times entering different names to verify thatitis correctly.

Experiment

Lines10and 40ofthe previous program will be changed to

10

INPUT

l10

PRINT

The word YOUR must be insertedinboth linesasshown above. This will be done using the Editor.

Type the command

ED

IT

(ENTER)

#2

"YOUR "YOUR

Inserting a Word

NAME"; AGE

IS";

NS

AG

executing

to enter the Edit Mode.

72

The following will be displayed:

10

20 30

40

50 60

INPUT READ

IF

PRINT

DATA

"NAI"IE";

AS, AG-4

A$<>N$

"AGE

DAN, BETTY,

THEN

IS",

32,

35,

NS4i

GOTO

RON,

38,

RALPH,

LINDA, 29,

SKIP,

42~

3~

The cursorisplaced over the 1 in line cursor is directly over the letter N in the word NAME.

Line

10

should appear

Type in the word YOUR followed by a space. Line10should now appear

10

INPUT

Line10is A

of careful nottopress any other keys while you are moving the cursor. When you have the cursor positioned correctly, line 40 should appear

The cursor is positioned correctly for the insertion,sotype the word:

nowinthe desired form. Next, the cursor mustbepositioned on the letter

the word AGEinline 40. This can be done using the Cursor Movement keys.

'+0

F'R II\IT

as

"YOUR

NAME";NS

IS";

10.

Move the cursortothe nght so that the

as:

AG'-

as:

YOUR

followed by a space. Line 40 should now appear

l10

PRINT

At this point editing is finished, so you can exit from the Editor. Press

go

backtoBASIC or simply press

"YOUR

AGE

IS",

CfID.

AG

as:

(ESC)

twice to

Be

List the programtoconfirm that it is:

10

INPUT

20

READ

30

IF

l10

PRINT

50

DATA

8~

DATA

Note that lines10and 40 contain the desired changes.

AS,

AS

DAN,

BETTY,

"YOUR

AG

< >

"YOUR

NAME";

N$

AGE

32,

35,

THEN

RON,

RALPH,

IS",

N$

GOTO

AG

38,

73

20 LINDA,

29,

l12

SKIP,

3

Execute the program. You will have to enter one of the names listed in the Data statements, or an

N

,0.

1'1

f:::

YOUR Ok

?

RON

AGE

OutofData

If3

error will occur. Hereisan exampleofthe

~.m

output:

•

Execute the program several times, entering different names.

Experiment

In

additiontoinserting a character, the Editor can be used to delete a character. This

is

easily done and will be illustrated in this experiment. The variable AG in lines 20

and 40 of the previous program will be changed Type the command

ED

I T

(ENTER)

to

invoke the Editor. The following should be displayed:

10

INPUT "NAME";

30

IF

40

PRINT

50

DATA

60

DATA

The Ainthe variable arrow keys so that it is over the letter

#3

AS<>N$

"YOUR

DAN,

BETTY,

Deleting a Character

to

the single letter G.

N$

THEN

32,

AGinline 20 will be deleted first. Position the cursor with the

AGE

35,

GOTO

IS",

RON,

RALPH.

20~

AG

38,

LINDA,

29,

SKIP,

G.

Line 20 should appear

42~

as

Note that the cursor is positioned to the right of the character to be deleted. Now press CIKSf).

Notice that the letter A has been deleted to that the cursor

Line 20 will now appear as

as

desired and that the characters which were

the rightofthe deleted letter A have been movedtothe left one position. Also note

is

still positioned over the letter G.

74

Using the arrow keys, position the cursor over the letter Gofthe variable

40. When you have done this, line 40 should appear

40

Press

PRINT

(BKSP)

"YOUR

to

delete the letter A. Line 40 now should appear

AGE

IS!I~

as:

as

AG

in line

At this point, the editing is finished. Press

program to confirm it is:

10

INPUT

20

READ

30

IF

a0

PRINT

50

DATA

80

DATA

Execute the program to confirm that itisworking correctly. It

should be clcar that characters can bc easily deleted with the use of the Editor. You need only remember to position the cursor one character to the right be deleted.

Another very similar way to delete characters consists positioning the cursor right over the character you wish to delete and then pressing

(DEL)

(CSHIFT)(BKSP)).

As with

vacant space.

(BKSP),

Experiment

Hereisthe previous program againasit

"YOUR

NAME";

A$, G

A$

< >

N$

THEN

"YOUR

DAN,

BETTY,

characters to the right of the deletion will shift to the left to fill the

#4

AGE

32,

RON,

35,

Changing a Character

(ESC)

twice to exit from the Editor. List the

N$

GOTO

IS", RALPH,

20

G

38,

LINDA,

28,

SKIP,

of

currently existsinmemory:

42

3

of

the character to

entering the Editor,

10

INPUT

20

READ

30

IF

a0

PRINT

50

DATA

80

DATA

The commainline 40 will be changed to a semicolon so that the age will be printed closer to the phrase printed in the next field. The use space before the age. The change will be made with the Editor.

Enter the Editor with the command

ED

IT

(ENTER)

A$, G

A$

DAN, BETTY,

"YOUR

< >

"YOUR

NAME";

N$

THENGOTO

AGE

32,

RON,

35,

AGE

of

N$

20

IS",

RALPH,

IS."

a semicolon, however, will eliminate all but one

G

38,

LINDA,

28,

The comma specifies that the age will be

75

a2

SKIP,

3

Again you will see displayed:

,1~

2L'l

30

40

50

60

INPUT

F~EAD

IF PRINT DATA DATA

"NAME";

A~i.

A$<>N$

"YOUR DAN. BETTY,

(";:j

4!l

TI-·lE!\1

AGE

32.

35.

N$<IIi

GUrU

IS".

RON,

RALPH,

2(;.~1Ili

G

38.

LINDA, 29,

42

SKIP,

]~

....

Position the cursor so that itison the space preceding the variable Ginline 40. When

this

is

done, line 40 should appear

·4«:1

PRINT

Press

COkSP)

cursor. After this is done line 40 will appear as

40

PRINT

Note that the cursor IS still on the space which precedes G, thus itisin the correct position

to

insert the semicolon. Type a semicolon. Line 40 should now appear

"YOUR

on the keyboard. This will delete the character justtothe leftofthe

"YOUR

A<:iE

AGE

as

IS".

IS"

·4

4

as:

£10

PRINT

This is the desired formofline 40. You must remember that when character deleted will be the one just to the left ftrst, then the cursor will be positioned correctly for the insertion The operation can be carried out in the reverse order, but after the insertion, the cursor must be moved one position to the right before the deletion

Exit from the Editor by pressing the Escape key twice, or just hit

Execute the program several times to conftrm that itisworking correctly.

Experiment

List the previous program. You should see:

10 INPUT 20

READ

30

IF

£10

PRINT

50

DATA

80

DATA

A$t

A$

DANt BETTYt

"YOUR

#5

"YOUR

G

< >

"YOUR

AGE

15";

G

of

the cursor.Ifthe deletionisdone

Changing a Word

NAME"·;

N$

THENGOTO

AGE

32t

RONt

35t

N$

15";

38t

RALPHt

20

G

LINDAt 29t

SKIPt

is

£12

COKSP)

of

the new character.

done.

(fS).

3

is

used, the

76

In this experiment, the name RALPH in line 60 will be changed to MORT, with the use

of

the Editor. Enter the command

ED

IT

COO!ID

,

to activate the Editor.

it

is

Position the cursor in line 60 so that 60 should appear

60

DATA

Press

(BKSP)

appear

The cursoriscorrectly positioned for the insertionofthe new name. Type in the name

MORT. Line 60 should appear as

Line 60 isinits desired form; RALPH has been replaced by the name MORT. Exit from the Editor.

60

as:

DATA

as:

BETTY,

five times to delete the name RALPH. After thisisdone, line 60 will

BETTY,

35,

on the comma after the name RALPH. Line

RALPH.

MORT,

29,

SKIP.

SKIP,

List the program to confirm that it is:

10

INPUT

20

READ

30

IF

a0

PRINT

50

DATA

60

DATA

Execute the program. Here is an exampleofthe output:

N/",ME? 1'10RT

YOUR AGE

Ok

These experiments have illustrated how the Editor allows a character or characters to

be inserted, deleted or changed in a program without retyping any lines. With a little practice you will become quite adept at using the Editor to make necessary changes to your program.

A$, G

A$

DAN, BETTY,

"YOUR

< )

"YOUR

IS

29

NAME",

N$

AGE

32,

35,

THEN

RON,

MORT,

N$

GoTo 20

IS";

38,

G

LINDA,

28,

SKIP,

az

3

77

Experiment

#6

Changing Line Numbers

Delete the previous program from working memory with the NEW command. The following program allows

keyboard. When a zero in entered, the average

an

arbitrary listofnumbers to be entered from the

of

the non-zero numbersiscomputed

and displayed. (At least that is what the program should do.) Type the program exactly

10

INPUT

20

CT

=

CT

30 40 50 80

AI) =

IF

GOTO

PRINT

Al,l

N=0

10

as

it is listed:

"NUMBER";

+ 1

+ N

THEN

"At,lERAGE

GDTO

N

IS";

80

AI)/CT

The program accumulates the sumofthe numbers in the variable AV. The variable CT

is

a counter that records the numberofvalues entered.Ifthe number entered

then the averageisprinted in line Hereisan

exampleofthe executionofthe program:

NUMr.ER? NUMBt::rp

NUMBE:F~?

AVE

H/7iGE

'i-

~2

el

IS

:2

6@.

Ok

is

@,

Obviously, the programisnot working correctly. The averageofthe two numbers is 3, not 2. The reason for the inaccuracy is that the number

0 was counted by the

variable CT.

be

The program can check for a zero value for N is done before the number N

correcled by inlerchanging lines 20 and 40. In this way, the

is

counted. One way

of changing the orderofthe statementsisto retype the two lines. However,aneasier methodisto

use the Editortochange the line numbers.

Use the command

ED

I T

(ENTER)

to enter the Edit Mode.

78

Thc following will be displayed:

10

20

30

40

:)(2)

60

INPUT

CT CT

f\'V

IF

GOTO PRINT

"NUMBER";

"-:::

,I;'..}

N : 0

1

"AVERAGE

,;"

+-

THEN

1

GOTO

IS";

60~

A'V/CT

The line number 20 must be changed to 40 and the old line number 40 must be

to

changed appear

20. Movc the cursor to the 0 in line 20. When this is done, line 20 should

as:

CT

::"

CT

+-

The cursorispositioned correctlytochange the 2toa 4. Delete the 2 by pressing

~.

appear

Then insert the 4 by pressing

as:

CIJ

on the keyboard. Now the program should

10

1.1-121

:]

(Z!

40

5(;~

60

INPUT

CT

/':'.o,'..)

IF

ClOTO

PRINT

"NUMBER";

(:'1"

:::::

Nt

N =

:I.

"AVERAGE

+ l +-

(2)

THEN

GOTO

IS";

60

AV/CT

Next, move the cursor down two lines so that itisover the zeroofline 40. The line should then appear

as

79

Delete the 4 by pressing (IKIf), then insert a 2 by typing appear

Although the lines are not listedinthe correct order, theydohave the correct line numbers.

Exit from the Editor. List the program. You will see:

as:

10

INPUT "NUMBER"; N

.t.~0

CT

-",

CT'

'+

:3~!l

i~

I,.)

::::

A

',,/

+ N

20

IF

SQ)

(,01'0

6(21

PRINT'

10

INPUT 20 IF 30

AV=AV

40

CT

:'50

GO

60

PRINT

N = 0

N=0 =

TO

THEN

l(;.i)·~

"I\'·/ERASE

"NUMBER";

THEN

+ N

CT

+ 1

10

"AVERAGE

1.

~

GoTo

GOTO

It3";

N

IB";

604

AV/Cr

60

AV/CT

tIl.

The program will

The programislistedinthe correct order, because BASIC always lists the lines in your program according to their line numbers.

Here is an example of the execution of the program:

l\,IUMBER7

"JlJM]~,E:R?

NUI"IBER7 0

AVEH/,(;[

L~

::;::

IS

2

Ok

•

The program seems to be working correctly. Execute the program several times to verify that it will work correctly in every case.

You

will find that the abilitytomove a line in your programtoa different position by

is

changing the line number

very useful and convenient.

80

Experiment

It

is possibletomove a word or even a phrase from one place in your program another with the Editor. This can be very useful when you wanttoadd a line, or a portion of a line to another line.

List the last program

10

INPUT

20

IF

30

AV=AV

£10

CT

50

GOTO PRINT

60

The statement in line 40 will be placed in line 20, and line 40 eliminated. The revised program will be

10

INPUT

20

IF

30

AV=AV

50

GOTO

PRINT

60

Enter the EDIT command.

#7

to

"NUMBER";

N=0

THEN

=

CT

10

"AVERAGE

as

follows:

"NUMBER";

N=0

THEN

10

"AVERAGE

Changing a Phrase

confirm thatitis:

N

GOTO

+ N

+ 1

GOTO

+ N

60

IS";

N

IS";

60

AV/CT

ELSE

AV/CT

CT=CT

to

+ 1

l"i·~

1<4

THEN

as:

N~

GOTO

1i

IS

GOTO

GOTa60

604

;

6~~

AV/

as:

as

ELSE.

The program will be displayed

10

INPUT "NUMBER";

20

IF

N = 0

31~~

t;V

"'"

'+0

CT

:::::

::~i(21

GOfO

6~

PRIN'r

First the word ELSE will be added to line 20. Position the cursorinline 20 over the carriage return character. Line 20 should appear

20

IF

N =

The cursorisnow positioned for the insertionofthe word ELSE. Type a space and then the word ELSE. Line 20 should appear

20

IF

N =

Next, the statementinline 40 must be inserted after the word ELSE in line 20. This accomplishedasfollows: Position the cursorinline 40asfollows

THEN

l'lV +

CT

-+

:l

IIAVERA(3E

(2)

is

'"

cr

+.

:l

81

The cursor is placed on the first character (a space)tobe moved. Press the

SELECT

Function Key (Cfl)) on the top row of the keyboard. Move the cursortothe right

by pressing

8 until

itisover the carriage return characteratthe endofline 40.

As

the cursor moves, you will note that the characters are printed in reverse video (light

to

on dark). This indicates which characters are going appear

as

be moved. Line 40 should

Press the CUT Function Key

disappear from the screen. Line 40 should now appear

(~).

When youdothis, the characters marked will

as:

The characters to be movedtoline 20

CT

=

CT

+ 1

which no longer appear on the display have been movedtoa temporary storage area

the computer called the

done above,iscalled a

"PASTE

"cut."

buffer."

The operationofdeleting characters,

as

The remaining charactersinline 40, namely the number 40 and the carriage return,

to

will now be deleted. Position the cursor so that it is

the right of the carriage return

character.

£1121.

Press

(BKSPl

three times. This deletes what was leftofline 40. Since

of

instead in

the "PASTE buffer."

using a

"SELECT"

Your program should appear

1.G1I !'.IPUT

20

IF

3~1

,':;\.,1

50

GOTO

60

PRINT

II

j\IU!'IBEr~

N = 0

~,

AI)

..;-

10~

"AVERAGE

THEN

N~.

as:

and

Ii;

GOTO

IS";

"CUT"

N

60

operation, these characters are not saved

ELSE

AV/CT.

(BKSPl

was

used,

in

The only remaining operationisto insert the characters savedinthe PASTE buffer into line 20. Position the cursor in line 20 over the carriage return character. When

is

done, line 20 will appear

this

as

82

To insert the characters in the paste buffer, press the PASTE Command key on the

as

keyboard. When this is done, the characters will be inserted now appear

20

:I.+-

.

IF

as:

N - 0

THEN

GOTO

60

ELSE

CT

desired. Line 20 will

-

CT

+

The movementofThe

SELECT, a After the cut operation, the characters remain in the paste buffer and can be inserted

another partofthe programifdesired.

Exit from the Editor. List your program to confirm that it is correct:

10 20 30 50 60

Execute the program to confirm that it works as it did before.

CUT,

INPUT

IF Alj GDTD

PRINT

Experiment

characTers from one partofthe program to another requires a

and a PASTE.

"NUMBER";

N=0

THEN

=

AlJ

+ N

GOTO

N

60

ELSE

CT

=

CT

+ 1

10

"AljERAGE

IS";

AlJ/CT

#8

Copying a Phrase (without deleting it)

The previous program will be modified so that the sum of the numbers entered will be

as

printed before the average value is printed. The revised program will be

10

INPUT

20

IF

£10

AlJ=AV

50

GOTO PRINT

60 70 PRINT

"NUMBER";

N=0

THEN

10

"SUM "AljERAGE

+ N

GOTO

IS";

N

60

AlJ

IS";

ELSE

AlJ/CT

CT

=

CT

+ 1

follows:

in

Note that the previous line 60 is now line 70 and a new line 60 has been added. These changes will be made with the Editor.

Enter the command

EDIT

83

The program will be displayedasusual:

10

INPUT "NUMBER";

20

IF

1,q~

30

40

50

61ll

N = 0

AV-AV+N,,:! CT

--

CT

GOTO PRINT

10#~

"AVERAGE

THEN

+ 1

<ilI1

N.

GOTO

IS";

60

ELSE

AV/CT.

CT-CT

+

Since the new lines 60 and 70 are very similar, the easiest waytorevise the program istocreate a copyofline 60 and then make the necessary revisions.

Put the cursor on the 6 of line 60. Line 60 should appear

PRINT

Line 60isto

"AVERAGE

IS",

Al/lCT

....

be transfered to the paste buffer. Press the SELECT Function Key

as:

«(f7)).

After this is done, move the cursor down one line, so that it isonthe endoffile marker. Line 60 will now appear

as:

Note that the entire line is in reverse video, indicating that itisreadytobe transfered to

the PASTE buffer. This line should not be deleted when it is transferedtothe

so

buffer,

press the

deletes. Now line 60 appears

60

PfHNT

COpy

Function Key

as

II/WERAGE

ISII;

(~).

Remember that

A\lICT~

~

transfers and

The cursor is alreadyinthe correct place for the insertion,sopress the paste key. You

should

60

see:

PRINT

IIAVERAGE "AVERAGE

C:'"

,.j

I

ISH;

•

,

AV/CT'~

AV/CT~

The second line number 60 will now be changedtoa 70. Position the cursor over the

o

in

the second line number 60.

60

61

+.-

PRINT

"AVERAGE

"AVERt\GE:

18";

IS";

AV/CT

A\,1./CT

84

Press

(BKSP)

and then

CD,

to change the 6 to a7.These two lines will now appear as:

60

PI~I!\IT

70

P!~~I!'rf"

"

.c'\'-v'ERl\(;;iE

"

AVEI~AGE

I

.,.

1

F~If~

f"'~

H u

~~

t.\)/

,6,"/

i

'J

cr~

Line 70 is in the desired form. Move the cursor to line 60 so that it is on the space

after AVERAGE. Line60will appear as:

6iZ!

PRI

NT

II AVE

!'I;~jl:::.!'!lF!j"

Press

(BKSP)

until the word AVERAGE is erased. Then type in the word SUM. Line

60

will be:

60

PRINT

"SUM

IS";

The last step is to delete the characters

~:;"

~

AV/

"/CT"

,tV).I

CT.

at the endofthe line. Move the cursor

to the endofthe line so that it is over the carriage return character 0

r

1>

FjR

I

I,.,oor

Press

6

60

l,(J

~

PRINT

"CUlv' I

i~

-...J

three times to erase the characters. Line 60 will be in the desired form

"8UM

Co".

A'

J i

11

•

~_,

~

IS";

.

\0'.'

Av4

('OOf".·"··

'-'

. .

Exit from the Editor. List the program to confirm that it is:

1121

INPUT

2121IFN=12I

1112l

AV=AV

5121

GOTO

SI2I

PRINT

7121

PRINT

"NUMBER";

THEN

GOTO

+ N

1121

"SUM

IS";

"AVERAGE

N

SI2I

AV

IS";

ELSE

AV/CT

CT

=

CT

+ 1

Execute the program. Here is an exampleofthe output:

NUMBER? NUMBER'7 2 NlJl"IJ3ER? 0 SUi'1TE)

A\,JE

::-~ACiEI~3

·4

6

3

Recall thatifa BASIC program isSAVEd in RAM but changes are made to it when the program is LOADed in working memory, the program SAVEd in RAM will reflect those changes0

85

This is true alsoofthe Editor.Ifthe Editorisused to modify a program which was

in

previously SAVEd You should practice using the Editor to modify your programs.

a very convenient and quick way

RAM, then these changes also appearinthe SAVEd program.

Yau

will find that it is

of

making changes.

What you have learned:

You have learned how to use the Editor to modify your cases,

it

is easier and quicker to make changes with the Editor, than to make them by

retyping entire lines.

BASTC

programs.Inmost

86

Lesson

In this Lesson, you will learn how to create a program loop with a predetermined number variables, which will also be introduced in this lesson.

of

#7

repetitions. This is a useful technique when combined with subscripted

Sales Trend

Experiment

The program below is a "Sales Trend" program. Its purpose istohelp predict future sales based upon the trend to

find a straight line which best fits the historical data and thentoproject this line

into the future. Clear working memory with the NEW command and enter the following program:

10

CLS

20

INPUT

30

FOR

110

PRINT

INPUT

50 60

SX

70

SY

80

100 110 120

Execute this program. The program begins by asking you

data. Type 6 and press The program then prompts you for the sales data for each of the six time periods.

Enter the following sales data:

;;;

B

A

PRINT PRINT

#1

Sales Trend

of

previous sales. The concept underlining this program is

"NUMBER

X

1

=

"SALES

TO

OF N FOR

Y

SX

+

= =

SY

+

X:XX Y:XY

X

(N*XY-SX*SY)

;;;

(SY

-

B*SX) "FORECAST A;

(ENTER).

II

"

+

PERIODS";

N

PERIOO";X;

XX

+

=

XY

=

/ N

FOR

;

B;

..

to

enter the numberofperiodsofhistorical sales

+

/

(N*XX PERIOD

X"

*

X*X X*Y

SX*SX)

-

X IS"

SALES

SALES SALES SALES SALES SALES

The formula for a straight line

Y = A +

where Y stands for Sales and X for the time period number. Aiscalled the "intercept"

FOR FOR FOR FOR FOR FOR

B*X

and B the

PERIOD PERIOD PERIOD PERIOD PERIOD PERIOD

"slope"ofthe line. The program uses the sales data which

is:

17 27 37

117

57 6?

103 110 108

120 118 133

87

you have just entered to compute the valuesofA and B.Ifyou entered the data exactly as shown above, the program will print:

FORECAST

86.86666666666

You can now use this formulatopredict any future period sales by plugging an appropriate value for X. For example, to predict period 7 sales, enter the following from the keyboard:

PRINT

The resulting number, 134.467, represents the trend line forecastofperiod 7 sales. You can use the program to calculate the trend line formula for any number

periods and any sales data. Try running the program again with your own data. You can use any convenient time period you wish, such as day, week, month, quarter, or year.

How the Sales

Look at the listingofthe Sales Trend program and compare it to the flowchart in Figure 7-1.

Line

18 The CLS statement clears the display.

Line

28 The INPUT statement displays the prompt message "NUMBER OF PERIODS?" and then waits for data to be entered. The question mark is automatically added by the INPUT statement and should not be inserted within the quotes prompt message. When

to

assigned

the numeric variable N.

FOR

86.8667

PERIOD X

+

5.371QZ8571QZ86*X

+

5.371Q3

Trend

IS

* 7

Program

Works

of

time

the

mEID is pressed, the number which has been typed will be

Line

38 The

with successive values for the index variable X. You can think saying:

Perform the following statements with X equal to I. Then repeat the same

statements with X equal to 2. Continue repeating these same statements with

successively incremented values

statements when X becomes equaltothe upper limit N.

Since the variable N is INPUT during execution, this program can be used to compute a trend line for any number

The end When the NEXT X statement is encountered, the loop is repeated with the next value ofX.If following the NEXT statement.

In general, the FOR statement has an

The index variable must be a numeric variable. The start and stop values may be

constants, variables

30 FOR A = U TO

FOR

statement defines the beginningofa loop whichisto

of

X

(l,

2, 3, etc.). Stop repeating this loop

of

sales periods.

of

the loop is determined by a matching NEXT statement (see Line 80).

the upper limit N has been reached, execution continues with the statement

index variable, a start value and a stop value.

or

expressions. Another exampleofa FOR statement would be:

ZJ(Y

-2)

be repeated

this statement as

of

88

( Keyboard

)--

NUMBER OF

PERIODS?

Figure 7-1. Sales Trend Program Flowchart

89

In this case, the loop of statements would be executed first with the index variable A equal to the start value stored in the variable U. The loop would then be repeated with the index variable A incremented by 1, i.e. A

with increasing values for the variable A until the upper limit, determined

computing the valueofthe expression Z/(Y - 2),isreached.

to

There would have

statement to determine the end of the loop. After the last cycle through the loop with A having the value Z/(Y - 2), execution continues with the statement immediately after the NEXT A statement.

Lines

40 - 50 The PRINT statement prints the prompt message

SALES FOR PERIOD X

where the value of X first time through the loop, X has the value 1,

be a NEXT A statement located in the program after the FOR

is

determined by the previous FOR statement (Line 30). The

= U+

1.

The loop would be repeated

so

the prompt message prints

by

as:

SALES

The second time through the loop, X has the value 2, so the prompt message prints

SALES

Each time through the loop, the prompt message requests the appropriate period number because the variable X is being incremented in the FOR statement.

Note the use period number (X) will print immediately after the word semicolon tells the Computer not to move the cursor after printing the period number. This means that the question mark statement, will appear immediately after the period number.

The INPUT statement waits until a number this number in the variable the current period's sales amount.

60 • 70 These lines actually include two statements each. Line 60, for instance,

Lines includes two assignment statements separated by a colon(:). Line

written

The two statements were put on the same line strictly as a matter of convenience and

to illustrate that

number

in

60 SX = SX + X 65

FOR

PERIOD

FOR

PERIOD

of

semicolons in this statement. The first semicolon ensures that the

an equivalent manner with two separate line numbers

XX

= XX + X*X

Multiple Statements (two or more statements) can share the same line

if

they are separated with a colon.

1

2

"PERIOD."

(?), automatically printed by the following INPUT

is

entered from the keyboard and stores

Y.

The variable Y actsasa temporary storage location for

The second

60 could have been

as:

The formula for a straight line requires the summationofseveral quantities:

• the variable SX

• the variable XX X*X)

• the variable

• the variable XY

All variables in a program are initially set to zero by the RUN command. Each time through the loop, the variable X is incremented read in as that period's sales.

is

usedtostore the sum of the X values,

is

used to store the sum of the squared X values, (Le. sum of

SY

is usedtostore the sum of the Y values, and

is

usedtostore the sum of X times Y (i.e., the sum of X*Y.)

to

the next period number, and Y is

90

The first time through the loop, therefore, SX will be replaced with the sum of zero, the initial value stored in the variable SX, and one (the first period number). Similarly, XX will be replaced with the sum of zero and one times one. The variable

is

XX now has the value one. The variable SY

period'~

first

sales (103 in the example above), and the variable XYisreplaced with

the sum of zero and one times the first period's sales (again,

7-1

Table

below illustrates how the four variables SX,

replaced with the sum of zero and the

103

in the example).

XX,

SY

and XY sumupthe

appropriate quantities on each repetition of the loop:

Loop cycle

0 1 2 2 3 4 4 120 5 6 6

Line

80

The NEXT X statement determines the end of the loop of statements which

to

be repeated with successive values for the index variableX.So longasthe

are

X

0 0

I

Y

103

X*X

X*Y

0 0 0 0

1

103

110 4 220

3 109 9

16

119

5

133

Table 7-1. Sales Trend Line Calculations

25

36

327 480 595 798

SX

1 1 3 6

10 15 21

XX

5

14 30 442 1130 55 91

SY

XY

0 0 103 213

103 323

322 650 561

1725

694 2523

value of X is less than the upper limit specified in the matching FOR X statement, the

loop will start over again with the next value for

When X reaches its upper limit(Nin

this case), execution transferstothe statement

immediately following the NEXT X statement (line

There must be a NEXT statement to match every FOR statementina program; without a NEXT therefore no way to know when

Lines 90 . 100 The assignment statements compute the slope, B, and intercept, A,

:statement, there would be no way to determine the endofthe FOR loop. and

to

repeat the loop.

X.

90 in this case).

which define the straight line which best fits the sales data. The use of parentheses was

necessary in the expressiontoproperly compute the ratios:

B=

*XY

N<XX

SX * SY SX *SX

N

and

A=

SY

B *SX

N

Using the sample data entered above, A and B are computed

B

6 * 2523

21

* 694

5.37143

21*21

and

91

as:

)'

Lines

A=

118.128

694 - 5.37143 *

6

The PRINT statements display the resulting trend line equation:

21

96.8667

FORECAST FOR PERIOD X

96.86666666666 + 5.3714285714286 *X

Line 110 prints the text contained within the quotes:

"FORECAST FOR PERIOD X

Line 120 then prints the equation for the predicted salesinperiodX.Note the use of

to

the semicolons also that the A and B in this statement are not enclosed stored in the variables A and B are printed. All other items enclosed in quotes and are therefore string constants, which print out

specified within the quotes. Since Line 120

print. The FOR / NEXT statement pair introduced

to

need situation comes up regularly in computer programming, you will the FOR / NEXT pair quite often in your own programs.

The following experiments will give you a few more ideas for its application and show you that the FOR statement offers even more flexibility.

repeat the same set of procedures a predetermined number of times. Since this

Experiment

keep everything printed immediately adjacenttoone another. Note

is

the last statement in the program, execution terminates after the

#2

Arrays

IS

IS"

in

quotes,sothat the values

in

this statement are

eXflctly

in

this lesson is very useful when you

no

doubt wanttouse

as

This experiment will store the sales dataaspart of the Sales Trend program, rather

to

than ask you This will make it easier

it each time the program

Change the Sales Trend program

20 25

input it during execution.

to

try

is

run.

N

24

=

DIM

Y(24)

several experiments on the data without havingtoretype

by

entering the following lines:

40 50 70 200 210 220 230 240 250

READ BY

=

DATA DATA DATA DATA DATA DATA

VeX) BY

160, 155, 215, 225, 275, 300,

vex)

+

175, 215, 265, 220, 270, 350, 330,

:XY

140, 155,

265,

255, 315,

=

XY

X*Y(X)

+

230 225 325 280

3a5

380

92

LIST the program; you should now have:

10

CLS

20

N

;;

24

25

DIM

Y(24)

30

FOR

X

;;

1

TO

N

50

READ

60

SX

70

SY

80

B = (N*XY - SX*SY) /

100 110 120

200 210 220

230

240

250

Suppose the data in lines 200 through 250 represent quarterly sales figures for six

consecutive years. RUN the program to compute the trend line on the 24 quarters data. You will not have to enter any data during execution, since the program reads the data from the DATA satements. correctly, you will see the trend line equation:

Y(X)

=

SX

=

+ X:XX =

SY

+

Y(X):XY

XX

=

X

A = (SY - B*SX) / N

PRINT "FORECAST PRINT DATA160, DATA DATA DATA DATA DATA

Aj"

155, 215, 225,

275,

300,

+

175, 215, 265, 220,

270, 265, 350, 330,

"j6j"

FOR

*

1.40,

155,

255, 315,

If

you have entered the program changes and data

+

X*X

XY

+ X*Y(X)

(N*XX

PERIOD X X" 230 225

325

290

345

380

- SX*SX) IS"

of

FORECAST FOR PERIOD X IS

148.22463768116

Of

course, the time period assumed here is a quarter, so that the equation will predict the sales for a specified quarter in the future. For example, to predict the first quarter of

year seven (period 25), enter:

PRINT

(The numbers are rounded

which is displayed represents the trend line projection

future.

A new type experiment. While this experiment could have been performed without the use subscripted variable, including it now will make the next experiment much easier.

The DIM Y(24) statement in line having a maximum can be thought

YO),

The number within the parentheses is called the SUbscript, and refers to the relative position corresponding DIM (for called the Y position X within the Y array.

148.225

of

variable, the

of

Y(2), Y(3),

of

the variable within the blockofstorage locations set aside by the

array.

+ 8.4086956521739 * X

+

8.4087

off

to three or four decimal places.) The result, 358.4425

subscripted

25

of

24 storage locations allocated to it. These 24 storage locations

as 24 separate variables:

....

Y(24)

"DIMension")

Thus, the variable Y(X), used in lines50and 70, refers to

*

25

of

sales to the next period in the

variable,

defines the variable Y as a subscripted variable

statement. The blockofstorage locations is

has been introduced in this

of

a

93

Line 50 will read the next data item from the OATA statements and store it in position X of the Y array. Since the FOR statement repeats line from 1 to 24, the data items will be stored in positions 1 through 24

50 with X assuming values

in

the Y array.

Each time through the loop, the assignment statements in line

-in

stored

the next location in the Y arraytocompute the sums SY and XY.

70 will use the value

Note that the Y array will contain all 24 data values when the program terminates. The next experiment will make use of this feature.

Experiment

#3

Seasonal Data

Frequently, sales data exhibit seasonal characteristics. For example, the first quarter might traditionally be slow compared to the rest of the year.

to

might be useful

modify the trend line forecast by the amount that the quarter

If

this is the case, it

is

typically above or below the trend. The amount above or below the trend is called the

"ratio to trend" and

is

determined by comparing the historical (actual) sales for the quarter to the amount which the trend line would have predicted for that period.

Since there are six years of data, and take the average (sum the ratios and divide by six). This

ratio to trend

and is the amount that sales in the first quarter differ, on the average,

we

compute the ratio for each of the first quarters

is

called the average

from the trend line. Figure 7-3 illustrates the ratio to trend for quarter I using the example data introduced

in Experiment 2 above.

Legend

*

Y.

Actual Sales

• Y,Computed Trend Sales

+ Seasonally Adjusted Forecast

Y R Ratio to Trend

$ Sales Y

R Average Ratio to Trend

~

,

400

300

200

148.2

100

156.6

I

R-1.02

1

YEAR 1

5

YEAR 2

9

YEAR 3

13

YEAR 4

17

YEAR 5

Figure 7·3. Illustration of Ratio to Trend

94

21

YEAR 6

25

Period

Number

Radio Shack TRS-80 Model 100 Basic Manual

Specifications and Main Features

Frequently Asked Questions

User Manual