Enter BASIC

BASIC was invented by two Dartmouth College professors (John Kemeny and Tom Kurtz) in 1964. Later they improved it. Now BASIC consists of words such as PRINT, INPUT, IF, and THEN.

Here’s how to program the computer by using those BASIC words.

Microsoft BASIC

Since Microsoft BASIC is so wonderful, all the popular computer companies paid him to make their computers understand Microsoft BASIC. That’s right: IBM, Apple, Commodore, Tandy, Atari, Texas Instruments, and hundreds of other computer companies all had to pay off Bill.

Microsoft BASIC has become so popular that Bill had to hire hundreds of employees to help him fill all the orders. Microsoft Incorporated has become a multi-billion-dollar company, and Bill has become a famous billionaire, the wealthiest person in America.

What’s QBASIC?

Over the years, Bill gradually improved Microsoft BASIC. Some computers use old versions of Microsoft BASIC; other computers use his latest improvements.

If you’re using Windows 95, you can use QBASIC if your computer used to have MS-DOS 5, 6, 6.2, 6.21, or 6.22 or if your copy of Windows 95 came on a CD-ROM disk.

What’s in this chapter?

This chapter explains how to use QBASIC. The chapter ends with an appendix (on pages 438-449) explaining how other versions of BASIC differ.

The chapter includes 8 sections:

Enter BASIC 330

Math 334

Strings 336

Tricky printing 337

File menu 339

Become an expert 340

Going & stopping 341

What’s a variable? 346

INPUT 349

IF 353

SELECT 355

Fancy IF conditions 357

Exiting a DO loop 359

FOR…NEXT 360

DATA…READ 363

Variables & constants 369

Loop techniques 370

Debugging 374

Error messages 375

PAUSE key 376

F keys 376

Apostrophe 377

Zones 378

TAB 380

LOCATE 382

Pixels 382

Sounds 385

PRINT USING 386

Exponents 388

Contrasts 389

Clock 390

Stripping 392

Random numbers 394

Character codes 398

String analysis 400

Trigonometry 402

Types of numbers 403

Subscripts 408

SUB procedures 412

Design a program 416

Make it efficient 418

Test it 418

Document it 419

Fancy input 420

SWAP 423

Sequential data files 426

Random access 428

Create a database 430

SHELL 434

ON ERROR GOTO 435

Memory cells 437

QBASIC 438

Quick BASIC 438

Visual BASIC for DOS 439

Visual BASIC for Win. 440

GWBASIC 444

Other computers 449

QBASIC’s commands are explained on these pages:

QBASIC’s functions are explained on these pages:

QBASIC’s F keys are explained on these pages:

F2 SUB show a different SUB 412

F4 View switch between blue & black screens 333

F5 Continue continue running the program 376

SHIFT F5 Run run the entire program 332

F6 Immediate move to & from immediate window 376

F7 Above run the program down to here 377

F8 Step run one more line of the program 377

F9 Breakpoint create or destroy a red breakpoint 376

Start QBASIC

To start using QBASIC, turn on the computer without any floppy in drive A.

Make sure the screen shows this standard C prompt:

C:\>

(To make the screen show it, follow the instructions on pages 100-101 of the MS-DOS chapter. Those instructions work even if you’re using Windows 3 or 3.1 or 3.11 or 95. For more details about making Windows 95 show the C prompt, read page 160’s "DOS Commands". For more details about making earlier versions of Windows show the C prompt, read page 148’s "Choose from a menu".)

C:\>qbasic

When you press the ENTER key at the end of that line, see what happens!

If you’re lucky, the screen will turn blue and the computer will say:

Welcome to MS-DOS QBASIC

If you’re unlucky, the computer will gripe by saying "Bad command or file name". To find out why the computer is griping, type "ver" after the C prompt. Then the computer will tell you which version of DOS it’s using. To run QBASIC, you must buy DOS version 5, 6, 6.2, or 6.22 (since QBASIC is not included with DOS versions 6.1 or 6.3 or 7), or buy the CD-ROM version of Windows 95 and copy QBASIC from that CD-ROM to your hard disk as follows:

Insert the Windows 95 CD-ROM disk (which some computer makers call the "Windows 95 Companion Disk").

If that disk’s window is on the screen, close the window by clicking its X box. Make sure the computer says "C:\>" (by following the instructions on page 160). Then type:

copy d:other\oldmsdos\qbasic.* windows\command

(After the asterisk, make sure you put a space. If your CD-ROM drive is called "drive E" instead of "drive D", type "e:" instead of "d:".)

Then try again to type "qbasic" after the C prompt.

Type your program

Now you’re ready to type your first program!

For example, type this program:

CLS

PRINT 4 + 2

Here’s how. Type CLS, then press the ENTER key at the end of that line. Type PRINT 4 + 2 (and remember to hold down the SHIFT key to type the symbol +), then press the ENTER key at the end of that line.

Notice that you must press the ENTER key at the end of each line.

Run your program

The computer will begin by obeying the CLS command. The computer will clear the screen and make the screen become all blank, all black.

Then the computer will obey the PRINT 4 + 2 command. The computer will print this answer onto your screen:

6

Congratulations! You’ve written your first program! You’ve programmed the computer to compute the answer to 4 + 2! You’ve become a programmer! Now you can put on your resumé: "programmer!"

CLS

PRINT 4 + 2

If you’d like to peek at the answer again (which is 6 on a black screen), press the F4 key again. When you finish peeking at the answer, press the F4 key again to view the program again (CLS and PRINT 4 + 2 on a blue screen).

So here are the rules:

To run the program (and put the answer on a black screen), press SHIFT with F5.

To view the blue screen again — or switch back to the black screen again — press F4.

Faster typing

?4+2

Think of the question mark as standing for this word:

What’s

If you want to ask the computer "What’s 4+2", type this:

?4+2

When you run the program, the computer will print the answer, 6.

Why CLS?

The program’s top line (CLS) tells the computer to erase the screen before printing the answer (6).

Edit your program

After you’ve typed your program, try typing another one. For example, create a program that makes the computer print the answer to 79 + 2. To do that, make this program appear on the screen:

CLS

PRINT 79 + 2

To make that program appear, just edit the program you typed previously (which said PRINT 4 + 2). To edit, use the arrow keys to move to the character you want to change (which was the 4), delete that character (4) by pressing the DELETE key, then type the characters you want instead (79).

While editing, use these tricks.…

To delete a character:

move the cursor (blinking underline) to that character, then press the DELETE key.

To delete SEVERAL characters:

move to the first character you want to delete, then hold down the DELETE key awhile.

To delete AN ENTIRE LINE:

move to that line; then while holding down Ctrl key, tap the Y key.

To INSERT A NEW LINE between two lines:

move to the beginning of the lower line; then while holding down Ctrl key, tap the N key.

CLS

PRINT 79 + 2

and you do not see the old program anymore.

When you’ve finished editing the program, run it (by pressing SHIFT with F5 again). Then the computer will print the answer:

81

Fix your errors

What happens if you misspell a computer word, such as CLS or PRINT? For example, what happens if you accidentally say PRIMPT instead of PRINT?

When you run the program (by pressing SHIFT with F5), the computer tries to run each line of your program. If the computer comes to a misspelled computer word (such as PRIMPT), the computer highlights your misspelling (by showing it in blue letters against a white background) and says:

Syntax error

Press the ENTER key, then fix your error, then try again to run the program (by pressing SHIFT with F5 key again).

Math

This command makes the computer add 4 + 2:

PRINT 4 + 2

Put that command into a program (whose top line should be CLS). When you run the program (by pressing SHIFT with F5), the computer will print the answer:

6

If you want to subtract 3 from 7, type this command instead:

PRINT 7 - 3

(When typing the minus sign, do not press the SHIFT key.) The computer will print:

4

You can use decimal points and negative numbers. For example, if you type this —

PRINT -26.3 + 1

the computer will print:

-25.3

Multiplication

To multiply, use an asterisk. So to multiply 2 by 6, type this:

PRINT 2 * 6

The computer will print:

12

Division

To divide, use a slash. So to divide 8 by 4, type this:

PRINT 8 / 4

The computer will print:

2

Huge & tiny numbers

When dealing with huge and tiny numbers, be careful!

For example, suppose you want the computer to multiply 200 by 300. Since the answer to that problem is 60 thousand, which is bigger than 32 thousand, you should put a decimal point in that problem. But suppose you forget to insert a decimal point, and you say just this:

CLS

PRINT 200 * 300

the computer will complain by saying:

Overflow

When the computer says "Overflow", reply by pressing the ENTER key, then fix your program by inserting a decimal point, like this —

PRINT 200 * 300.0

or like this —

PRINT 200 * 300.

When you finish typing that line (and press ENTER afterwards), the computer will do something strange: it will turn the ".0" or "." into an exclamation point, so the line looks like this:

PRINT 200 * 300!

When you run the program, the computer will print the right answer:

60000

Notice that if you type a decimal point at the end of a number, the computer usually puts an exclamation point (!) at the end of the number. If the number is long, the computer puts a number sign (#) instead of an exclamation point.

For example, suppose the computer says the answer to a problem is:

8.516743E+12

So when the computer says the answer is 8.516743E+12, the computer really means the answer is 8516743000000, approximately. The exact answer might be 8516743000000.2 or 8516743000000.79 or some similar number, but the computer prints just an approximation.

Suppose your computer says the answer to a problem is:

9.23E-06

After the E, the minus sign means, "towards the left". So look at 9.23, and move the decimal point towards the left, 6 places. You get:

So when the computer says the answer is 9.23E-06, the computer really means the answer is:

You’ll see E notation rarely: the computer uses it just if an answer is huge (many millions) or tiny (tinier than .01). But when the computer does use E notation, remember to move the decimal point!

100000000000000000000000000000000000000

If you try to go much higher, the computer will either gripe (by saying "Overflow") or use D notation (which goes up to about 1D308).

.00000000000000000000000000000000000001

If you try to go much tinier, the computer will either say 0 or use D notation (which goes down to about 1D-323).

Order of operations

What does "2 plus 3 times 4" mean? The answer depends on who you ask.

To a clerk, it means "start with 2 plus 3, then multiply by 4"; that makes 5 times 4, which is 20. But to a scientist, "2 plus 3 times 4" means something different: it means "2 plus three fours", which is 2 + 4 + 4 + 4, which is 14.

Since computers were invented by scientists, computers think like scientists. If you type —

PRINT 2 + 3 * 4

the computer will think you mean "2 plus three fours", so it will do 2 + 4 + 4 + 4 and print this answer:

14

The computer will not print the clerk’s answer, which is 20. So if you’re a clerk, tough luck!

PRINT 2 + 3 * 4

the computer begins by hunting for multiplication and division. When it finds the multiplication sign between the 3 and the 4, it multiplies 3 by 4 and gets 12, like this:

PRINT 2 + 3 * 4

So the problem becomes 2 + 12, which is 14, which the computer prints.

For another example, suppose you type:

PRINT 10 - 2 * 3 + 72 / 9 * 5

The computer begins by doing all the multiplications and divisions. So it does 2 * 3 (which is 6) and does 72 / 9 * 5 (which is 8 * 5, which is 40), like this:

PRINT 10 - 2 * 3 + 72 / 9 * 5

6 40

So the problem becomes 10 - 6 + 40, which is 44, which is the answer the computer prints.

PRINT 5 - (1 + 1)

the computer will compute 5 - 2 and print:

3

You can put parentheses inside parentheses. If you type —

PRINT 10 - (5 - (1 + 1))

the computer will compute 10 - (5 - 2), which is 10 - 3, and will print:

7

Strings

Let’s make the computer fall in love. Let’s make it say, "I love you".

Type this program:

CLS

PRINT "I love you"

When you run the program (by pressing SHIFT with F5), the computer will obey your command; it will print:

I love you

You can change the computer’s personality. For example, if you give this command —

PRINT "I hate you"

the computer will reply:

I hate you

PRINT "aieee luf ya"

the computer will still copy the message (without worrying about what it means); the computer will print:

aieee luf ya

Faster typing

Instead of typing —

PRINT "I love you"

you can type just this:

?"I love you

At the end of that line, when you press the ENTER key, the computer will automatically do three things:

The computer will replace the question mark by the word PRINT.

The computer will put a blank space after PRINT (and before the quotation mark).

The computer will put a quotation mark at the end of the line (to match the other quotation mark).

Jargon

Strings versus numbers

Accidents

Suppose you accidentally put the number 2 + 2 in quotation marks, like this:

PRINT "2 + 2"

The quotation marks make the computer think "2 + 2" is a string instead of a number. Since the computer thinks "2 + 2" is a string, it copies the string without analyzing what it means; the computer will print:

2 + 2

It will not print 4.

Suppose you want the computer to print the word "love" but you accidentally forget to put the string "love" in quotation marks, and type this instead:

PRINT love

Since you forgot the quotation marks, the computer thinks love is a number instead of a string; but the computer doesn’t know what number it is, since the computer doesn’t know the meaning of love. Whenever the computer is confused, it either gripes at you or prints a zero. In this particular example, when you run the program the computer will print a zero, like this:

0

So if you incorrectly tell the computer to proclaim its love, it will say zero.

Longer programs

You can program the computer say it’s madly in love with you!

Let’s make the computer say:

I love you.

You turned me on.

Let's get married!

To make the computer say all that, just run this program:

CLS

PRINT "I love you."

PRINT "You turned me on."

PRINT "Let's get married!"

To run that program, type it and then press the F5 key. Try it!

To have even more fun, run this program:

CLS

PRINT "I long"

PRINT 2 + 2

PRINT "U"

It makes the computer print "I long", then print the answer to 2+2 (which is 4), then print "U". So altogether, the computer prints:

I long

4

U

Yes, the computer says it longs for you!

Tricky printing

Printing can be tricky! Here are the tricks.

Indenting

Suppose you want the computer to print this letter:

Dear Joan,

Thank you for the beautiful

necktie. Just one problem--

I don't wear neckties!

Love,

Fred-the-Hippie

This program prints it:

CLS

PRINT "Dear Joan,"

PRINT " Thank you for the beautiful"

PRINT "necktie. Just one problem--"

PRINT "I don't wear neckties!"

PRINT " Love,"

PRINT " Fred-the-Hippie"

Blank lines

Life consists sometimes of joy, sometimes of sorrow, and sometimes of a numb emptiness. To express those feelings, run this program:

Altogether, the computer will print:

joy

sorrow

Semicolons

Run this program:

CLS

PRINT "fat";

PRINT "her"

father

This program gives you some food for thought:

CLS

PRINT "I love to eat her";

PRINT "ring for dinner";

PRINT "you are the most beautiful fish in the whole sea!"

The program says to print three phrases. Because of the semicolons, the computer tries to print all the phrases onto a single line; but those phrases are too long to all fit on the same line simultaneously! So the computer prints just the first two phrases onto the line and prints the third phrase underneath, like this:

I love to eat herring for dinner

you are the most beautiful fish in the whole sea!

The next program shows what happens to an evil king on a boat:

CLS

PRINT "sin"; "king"

The computer will print "sin", and will print "king" on the same line, like this:

sinking

Notice that in a PRINT statement, you can type several items (such as "sin" and "king"). You’re supposed to type a semicolon between each pair of items; but if you forget to type a semicolon, the computer will type it for you automatically when you press the ENTER key at the end of the line. The computer will also automatically put a blank space after each semicolon.

Spaces after numbers

Try typing this command:

PRINT -3; "is my favorite number"

-3 is my favorite number

­

space

Spaces before positive numbers

This command tells what to put in your coffee:

PRINT 7; "do"; "nuts"

7 donuts

­ ­

spaces

Hey, if you’re feeling cool, maybe this command expresses your feelings:

PRINT "the temperature is"; 4 + 25; "degrees"

The computer prints "the temperature is", then 4 + 25 (which is 29), then "degrees". Since 29 is a positive number, the computer prints a blank space before and after the 29:

the temperature is 29 degrees

­ ­

spaces

Fix the negative numbers

Use this command if you’re even colder:

PRINT "the temperature is"; 4 - 25; "degrees"

The computer prints "the temperature is", then 4 - 25 (which is -21), then "degrees". Since -21 is a number, the computer prints a space after it; but since -21 is not positive, the computer does not print a space before it. The computer prints:

the temperature is-21 degrees

­ ­

no space space

Yuk! That looks ugly! It would look prettier if there were a space before the -21. To insert a space, put the space inside quotation marks:

PRINT "the temperature is "; 4 - 25; "degrees"

­

inserted space, before the quotation mark

Then the computer will print:

the temperature is -21 degrees

­

inserted space

Multiple calculations

By using semicolons, you can make the computer do many calculations at once.

For example, this command makes the computer do 6+2, 6-2, 6*2, and 6/2, all at once:

PRINT 6 + 2; 6 - 2; 6 * 2; 6 / 2

That makes the computer print the four answers:

8 4 12 3

The computer prints spaces between the answers, because the computer prints a space after every number (and an additional space before every number that’s positive).

Print on paper

If you say LPRINT instead of PRINT, the computer will print on paper instead of on your screen.

For example, if you want the computer to compute 2+2 and print the answer on paper, type this program:

CLS

LPRINT 2 + 2

While typing that program, make sure you type "LPRINT". Although "PRINT" can be abbreviated by typing "?", "LPRINT" cannot be abbreviated by typing "L?"; you must type the word "LPRINT" in full.

When you run that program (by putting paper into the printer, turning the printer on, and pressing the F5 key), the computer will compute 2 + 2 and print this answer onto paper:

4

LPRINT CHR$(12);

That line works for all popular printers.

For example, this program makes the computer figure out the answer to 2+2, print the answer (4) onto paper, and then eject the paper from the printer:

CLS

LPRINT 2 + 2

LPRINT CHR$(12);

This program prints a poem on paper and then ejects the paper:

CLS

LPRINT "I see England."

LPRINT "I see France."

LPRINT "I see Batman's"

LPRINT "underpants!"

LPRINT CHR$(12);

If you want to print several copies of that poem onto paper (so you can hand the copies to several friends), run that program several times: each time, say run (by pressing SHIFT with F5) and return to the blue screen (by pressing F4).

After pressing the PRINT SCREEN key, eject the paper manually.

If you want to print several copies on paper, press the PRINT SCREEN key several times — and eject the paper manually each time.

WIDTH 40

At the top of your program, instead of saying CLS, you can say:

WIDTH 40

Though WIDTH 40 widens the computer’s answers on the black screen, it does not widen characters on paper or on the blue screen (where you type your program).

File menu

Here’s how to use it.…

Print

For example, if the screen shows this program —

CLS

PRINT 2 + 2

the printer will print this onto paper:

CLS

PRINT 2 + 2

Then eject the paper manually.

Save

Pick a name that reminds you of the program’s purpose. For example, if the program prints a bill to a customer, call the program "BILL"; if the program plays chess, call the program "CHESS"; if it gives a quiz, call it "QUIZ"; if it tutors a human about the elements of sex, call it "SEX"; if it tutors a human about advanced sex, call it "SEX2".

The name must be short (up to 8 characters long) and should be simple (consisting of just letters and digits).

When you finish typing the name, press the ENTER key. Then the computer copies your program to the hard disk.

For example, if you typed the name "joe", the computer copies your program to the hard disk and names the program "JOE.BAS". (Notice that the computer automatically capitalizes the name and puts .BAS afterwards. The .BAS means "written in BASic".)

Exception: if the name you invented was already used by another program, the computer asks you, "Overwrite?" Press the Y key if you want the new program to replace the old program, so the old program disappears. If you do not want the new program to replace the old program, press N instead of Y, then invent a different name for your new program.

To protect yourself against such a calamity, choose Save from the file menu every fifteen minutes. Then if your town has a blackout, you’ll lose just a few minutes of work; the rest of your work will have already been saved on the disk.

Saving your program every fifteen minutes protects you against blackouts and also again "computer malfunction" and any careless errors you might make.

New

If you didn’t save the program you worked on, the computer asks, "Save it now?" If you want to save the program you worked on, press the Y key; if you do not want to save the program you worked on, press the N key instead.

Open

The computer shows you an alphabetical list of all BASIC programs on the hard disk. (If the list is too long to fit on the screen, the computer shows you the list’s beginning.)

Then say which program you want, by using one of these methods.…

Method 1: type the name of the program you want (such as "joe"), then press ENTER.

Method 2: press the TAB key, then the down-arrow key; then press the down-arrow key a few more times until the program you want is highlighted; then press the ENTER key.

All lines of that program will appear on the screen.

(Exception: if a different program has been on the screen and you didn’t save it, the computer will ask, "Save it now?" If you want to save that program, press the Y key; if you do not want to save that program, press the N key instead.)

ESCAPE key

Save As

Here’s how to create a program called JOE, then create a variant of it called JOE2.

Exit

(If you didn’t save the program you worked on, the computer asks, "Save it now?" If you want to save the program you worked on, press the Y key; if you do not want to save the program you worked on, press the N key instead.)

Then the computer will exit from QBASIC, and the screen will say:

C:\>

Become an expert

Congratulations! You’ve learned how to program!

C’mon, write some programs! It’s easy! Try it. You’ll have lots of fun!

Write several programs like the ones I’ve shown you already. Then you can put on your resumé that you have "a wide variety of programming experience", and you can talk your way into a programming job!

The rest of this chapter explains how to become a good programmer.

Practice

If you have access to a computer, put this book next to the computer’s keyboard. At the end of each paragraph, type the examples and look, look, see the computer run. Invent your own variations: try typing different numbers and strings. Invent your own programs: make the computer print your name or a poem; make it solve problems from your other courses and the rest of your life. The computer’s a fantastic toy. Play with it.

If you’re a student, don’t wait for your instructor to give lectures and assign homework. Act now. You’ll learn more from handling the computer than from the lectures or readings. Experience counts.

Let me tell you the story of Charlie:

At Wesleyan University’s computer center, one of the directors was having trouble making the computer print the university’s payroll. He asked me for help, but I said I didn’t know either. I saw a little kid sitting at one of the keyboards. "Hey, Charlie," I called to him, "we’re having trouble getting the payroll out."

Little Charlie came over and typed some stuff on our keyboard. "The payroll will be out in a minute," he said gleefully.

Charlie was just in seventh grade. He’d never taken a computer course; his school didn’t offer one. But by spending the whole summer just "hanging around" our computer, he knew it better than we.

Be like Charlie. Hang around your computer. Communicate with it every day. At first, that will be even harder than talking with a cat or a tree, because the computer belongs to a different species, a different kingdom; but keep trying. Get to know it as well as you know your best friend.

If you’re taking a French course, you might find French difficult; and if you’re taking a computer course, you might find computers difficult also. But even a stupid three-year-old French kid can speak French, and even kindergarten kids can program the computer. They have just one advantage over you: practice!

Be bold

In science fiction, computers blow up; in real life, they never do. No matter what keys you press, no matter what commands you type, you won’t hurt the computer. The computer is invincible! So go ahead and experiment. If it doesn’t like what you type, it will gripe at you, but so what?

Troubles

When you try using the computer, you’ll have trouble — because you’re making a mistake, or the computer is broken, or the computer is weird and works differently from the majority computers discussed in this book. (Each computer has its own "personality", its own quirks.)

Whenever you have trouble, laugh about it, and say, "Oh, boy! Here we go again!" (If you’re Jewish, you can say all that more briefly, in one word: "Oy!") Then get some help.

Get help

For help with your computer, read this book! For further help, read the beginner’s manual that came with your computer, or ask the genie who gave you the computer (your salesperson or parent or boss or teacher or friend).

If you’re sitting near computers in your office, school, or home, and other people are nearby, ask them for help. They’ll gladly answer your questions because they like to show off and because the way they got to know the answers was by asking.

When dealing with the computer and the people who surround it, be friendly but also assertive. To make sure you get your money’s worth from a computer course, ask your teacher, classmates, lab assistants, and other programmers questions, questions, questions! If you’re using a computer that you own, get help from the person who gave it to you.

And remember — you can call me anytime at 617-666-2666, and I’ll help you, free!

Going & stopping

You can control how your computer goes and stops.

Instant open

Suppose you’ve saved a QBASIC program called JOE.

To use JOE, you could turn on the computer, then say —

C:\>qbasic

then choose Open from the file menu, then type "joe" (and press ENTER).

Here’s a faster way! Turn on the computer, then say:

C:\>qbasic joe

That makes the computer use QBASIC and instantly open JOE.

C:\>qbasic /run joe

That makes the computer use QBASIC, instantly open JOE, and automatically run JOE. Moreover, if JOE’s bottom line says "SYSTEM", like this —

CLS

PRINT "I love you"

SYSTEM

the computer will automatically exit from QBASIC when JOE finishes running.

Learn MS-DOS fundamentals (on page 114-130). Then read about "Batch files" (on pages 130-131), and practice the examples.

In a batch file, you can make one of the lines say:

qbasic /run joe

Then whenever you run that batch file, the computer will automatically run JOE.

SLEEP

If you say SLEEP, the computer will take a nap:

CLS

PRINT "I'm going to take a nap."

SLEEP

PRINT "Thanks for waking me up."

The second line makes the computer announce:

I'm going to take a nap.

The next line says SLEEP, which makes the computer take a nap. The computer will continue sleeping until you wake it up by pressing a key on the keyboard. (Press any key, such as ENTER.) Then the computer, woken up, will finish running the rest of the program, whose bottom line makes it say:

Thanks for waking me up.

CLS

PRINT "Valentine's Day, you didn't bring me flowers!"

PRINT "I won't speak until you gimme roses!"

PRINT "Bring them, then touch one of my keys."

SLEEP

PRINT "It's great to wake up and smell the roses!"

Lines 2-4 make the computer say:

Valentine's Day, you didn't bring me flowers!

I won't speak until you gimme roses!

Bring them, then touch one of my keys.

The next line (SLEEP) makes the upset computer go to sleep and refuse to talk to humans, until a human presses a key. When a human finally presses a key, the computer wakes up and says:

It's great to wake up and smell the roses!

That’s how to make the computer pause for 6 seconds. Give that 6-second pause before you reveal the punch line of a joke:

CLS

PRINT "Human, your intelligence is amazing! You must be an M.D.";

SLEEP 6

PRINT "--Mentally Deficient!"

That program makes the computer print the joke’s setup ("Human, your intelligence is amazing! You must be an M.D."), then pause for 6 seconds, then reveal the joke’s punch line, so the screen finally shows:

Human, your intelligence is amazing! You must be an M.D.--Mentally Deficient!

SLEEP 6 makes the computer sleep until it gets woken up by either the alarm clock (after 6 seconds) or the human (by pressing a key). If you want the computer to pause for 10 seconds instead of 6, say SLEEP 10 instead of SLEEP 6. The number after the word SLEEP can be 6 or 10 or any other positive whole number, but not a decimal.

This program makes the computer brag, then confess:

CLS

PRINT "We computers are smart for three reasons."

PRINT "The first is our VERY GOOD MEMORY."

PRINT "The other two reasons… ";

SLEEP 10

PRINT "I forgot."

The computer begins by bragging:

We computers are smart for three reasons.

The first is our VERY GOOD MEMORY.

The other two reasons…

But then the computer pauses for 10 seconds and finally admits:

I forgot.

This program makes the computer change its feelings, in surprising ways:

CLS

PRINT "I'm up";

SLEEP 3

PRINT "set! I want to pee";

SLEEP 4

PRINT "k at you";

SLEEP 5

PRINT "r ma";

SLEEP 6

PRINT "nual";

SLEEP 7

PRINT "dexterity. Touch me!"

The computer will print —

I'm up

then pause 3 seconds and change it to —

I'm upset! I want to pee

then pause 4 seconds and change it to —

I'm upset! I want to peek at you

then pause 5 seconds and change it to —

I'm upset! I want to peek at your ma

then pause 6 seconds and change it to —

I'm upset! I want to peek at your manual

then pause 7 seconds and change it to —

I'm upset! I want to peek at your manual dexterity. Touch me!

Experiment: invent your own jokes, and make the computer pause before printing the punch lines.

CLS

PRINT "If you can read this, you read quickly."

SLEEP 1

CLS

When you run that program, the computer makes the screen display this message:

If you can read this, you read quickly.

Then the computer pauses for 1 second (because of the SLEEP 1), then erases the screen (CLS). So the message appears on the screen for just 1 second before being erased!

If you manage to read that entire message in just 1 second, you’re indeed a fast reader!

But don’t stop at that first success! For the ultimate challenge, try running this program:

CLS

PRINT "Mumbling morons make my mom miss murder mysteries Monday morning."

SLEEP 2

CLS

That makes the computer display this tongue-twister —

Mumbling morons make my mom miss murder mysteries Monday morning.

then pause for 2 seconds, then erase the screen. During the 2 seconds while that tongue-twister appears on the screen, can you recite the entire twister out loud? Try it! If you don’t recite it properly, you’ll sound like a mumbling moron yourself!

DO…LOOP

This program makes the computer print the word "love" once:

CLS

PRINT "love"

This fancier program makes the computer print the word "love" three times:

CLS

PRINT "love"

PRINT "love"

PRINT "love"

When you run that program, the computer will print:

love

love

love

Let’s make the computer print the word "love" many times. To do that, we must make the computer do this line many times:

PRINT "love"

CLS

DO

PRINT "love"

LOOP

As you can see, put the line being repeated (PRINT "love") between the words DO and LOOP and indent it. (To indent, press the SPACE bar twice. To remove an indentation, put yourself just after the indentation and then press the BACKSPACE key.) When you run that program, the computer will do PRINT "love" many times and print:

love

love

love

love

love

love

love

love

love

etc.

The computer will print "love" on every line of your screen.

But even when the screen is full of "love", the computer won’t stop: the computer will try to print even more loves onto your screen! The computer will lose control of itself and try to devote its entire life to making love! The computer’s mind will spin round and round, always circling back to the thought of making love again!

CLS

DO

PRINT "love";

LOOP

The semicolon makes the computer print "love" next to "love", so the screen looks like this:

lovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelove

lovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelove

lovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelovelove

etc.

If you put a space after love, like this —

CLS

DO

PRINT "love ";

LOOP

the computer will put a space after each love:

love love love love love love love love love love love love love love love love

love love love love love love love love love love love love love love love love

love love love love love love love love love love love love love love love love

etc.

CLS

DO

PRINT "dog";

PRINT "cat";

LOOP

Lines 3 & 4 (which say PRINT "dog" and PRINT "cat") make the computer print "dog" and then print "cat" next to it. Since those lines are between the words DO and LOOP, the computer does them repeatedly — PRINT "dog", then PRINT "cat", then PRINT "dog" again, then PRINT "cat" again — so the screen looks like this:

dogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcat

dogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcat

dogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcat

etc.

The computer will keep printing "dog" and "cat" until you abort the program by doing this: while holding down the Ctrl key, tap the PAUSE/BREAK key.

To do that, flash "Stop pollution!" onto the screen for 2 seconds, then turn that message off for 1 second (so the screen is blank), then flash that message on again. Here’s the program:

WIDTH 40

DO

PRINT "Stop pollution!"

SLEEP 2

CLS

SLEEP 1

LOOP

The top line (WIDTH 40) makes sure all characters appear dramatically huge.

Lines 3 & 4 (which say PRINT "Stop pollution!" and SLEEP 2) flash the message "Stop pollution!" onto the screen and keep it on the screen for 2 seconds. The next pair of lines (CLS and SLEEP 1) make the screen become blank for 1 second. Since those lines are all between the words DO and LOOP, the computer does them repeatedly — flash message then blank, flash message then blank, flash message then blank — so your screen becomes a continually flashing sign.

The screen will keep flashing until you abort the program by doing this: while holding down the Ctrl key, tap the PAUSE/BREAK key.

Instead of saying "Stop pollution!", edit that program so it flashes your favorite phrase instead, such as "Save the whales!" or "Marry me!" or "Keepa youse hands offa my computer!" or "Jesus saves — America spends!" or "In God we trust — all others pay cash" or "Please wait — Dr. Doom will be with you shortly" or "Let’s rock!" or whatever else turns you on. Make the computer say whatever you feel emotional about. Like a dog, the computer imitates its master’s personality. If your computer acts "cold and heartless", it’s because you are!

I'm having trouble

with my nose.

The only thing it does is:

Blows!

Type this program:

CLS

DO

LPRINT "I'm having trouble"

LPRINT "With my nose."

LPRINT "The only thing it does is:"

LPRINT "Blows!"

LPRINT CHR$(12);

LOOP

Since it says LPRINT instead of PRINT, it prints each copy on paper instead of on the screen. Since the LPRINT lines are in a DO loop, the computer prints the poem again and again, many times, until you abort the program — or the printer runs out of paper.

Each time the computer prints a copy of the poem, the "LPRINT CHR$(12);" makes the computer eject a sheet of paper, so each copy of the poem is on a separate page.

Line numbers

You can number the lines in your program. For example, instead of typing —

CLS

DO

PRINT "love"

LOOP

you can type:

1 CLS

2 DO

3 PRINT "love"

4 LOOP

Then when you’re discussing your program with another programmer, you can talk about "line 3" instead of having to talk about "the line in the middle of the DO loop".

For example, if you’re planning to discuss just lines 2 and 4, you can number just those lines:

CLS

2 DO

PRINT "love"

4 LOOP

Or if you prefer, number them like this:

CLS

1 DO

PRINT "love"

2 LOOP

1 CLS

2 PRINT "Life's a blast!"

Suppose you want to edit it and insert an extra numbered line between 1 and 2. QBASIC lets you give the extra line a decimal number, such as 1.5:

1 CLS

1.5 PRINT "I hope..."

2 PRINT "Life's a blast!"

10 CLS

20 PRINT "Life's a blast!"

Then you can insert an extra line without using decimals:

10 CLS

15 PRINT "I hope..."

20 PRINT "Life's a blast!"

GOTO

This program makes the computer print the words "dog" and "cat" repeatedly:

CLS

DO

PRINT "dog";

PRINT "cat";

LOOP

It makes the computer print:

dogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcat

dogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcat

dogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcatdogcat

etc.

This program does the same thing:

CLS

10 PRINT "dog";

PRINT "cat";

GOTO 10

The second line (which is numbered 10) makes the computer print "dog". The next line makes the computer print "cat". The bottom line makes the computer GO back TO line 10, so the computer will print "dog" again, then "cat again", then GO back TO line 10 again, then print "dog" again, then "cat" again, etc. The computer will print "dog" and "cat" repeatedly, until you abort the program by pressing SHIFT with PAUSE/BREAK.

This program does the same thing:

CLS

joe: PRINT "dog";

PRINT "cat";

GOTO joe

CLS

PRINT "Let's munch"

PRINT "sandwiches under"

PRINT "the trees!"

It makes the computer print:

Let's munch

sandwiches under

the trees!

Let’s turn that dream into a nightmare where we all become giant termites. To do that, insert the shaded items:

CLS

PRINT "Let's munch"

GOTO 10

PRINT "sandwiches under"

10 PRINT "the trees!"

The computer begins by printing "Let’s munch". Then the computer does GOTO 10, which makes the computer GO skip down TO line 10, which prints "the trees!" So the program makes the computer print just this:

Let's munch

the trees!

Since the word GOTO is so powerful, programmers fear it! Programmers know that the slightest error in using that powerful word will make the programs act very bizarre! Programmers feel more comfortable using milder words instead (such as DO...LOOP), which are safer and rarely get botched up. Since the word GOTO is scary, many computer teachers prohibit students from using it, and many companies fire programmers who say GOTO instead of DO...LOOP.

But saying GOTO is fine when you’ve learned how to control the power! Though I’ll usually say DO...LOOP instead of GOTO, I’ll say GOTO in certain situations where saying DO...LOOP would be awkward.

Life as an infinite loop

A program that makes the computer do the same thing again and again forever is an infinite loop.

Some humans act just like computers. Those humans do the same thing again and again. Every morning they GOTO work, and every evening they GOTO home. GOTO work, GOTO home, GOTO work, GOTO home,… Their lives are sheer drudgery. They’re caught in an infinite loop.

Go to your bathroom, get your bottle of shampoo, and look at the instructions on the back. A typical bottle has three instructions:

Lather.

Rinse.

Repeat.

Those instructions say to lather, then rinse, then repeat — which means to lather again, then rinse again, then repeat again — which means to lather again, then rinse again, then repeat again.… If you follow those instructions, you’ll never finish washing your hair! The instructions are an infinite loop! The instructions are a program: they program you to use lots of shampoo! That’s how infinite loops help sell shampoo.

END

To make the computer skip the bottom part of your program, say END:

CLS

PRINT "She smells"

END

PRINT "of perfume"

When you run that program (by pressing SHIFT with F5), the computer will print "She smells" and then end, without printing "of perfume".

Suppose you write a program that prints a long message, and you want to run the program several times (so several of your friends get the message). If one of your friends would be offended by the end of your message, send that friend an abridged message! Here’s how: put END above the part of the message that you want the computer to omit — or skip past that part by saying GOTO.

Multi-statement line

CLS: PRINT "I dream": PRINT "of you"

When you run that program, the computer will CLear the Screen, then PRINT "I dream", then PRINT "of you". Altogether, the computer will print:

I dream

of you

If you want to number the line, put the number at the left margin, like this:

10 CLS: PRINT "I dream": PRINT "of you"