Fun

Imagine that you’re running for President against Calvin Coolidge. To win, you must pass Cal in the polls.

You must pass Cal. "Pass Cal" is the correct way to pronounce "PASCAL", the name of the computer language that programmers are falling in love with.

PASCAL is harder to learn than BASIC. But once you’ve learned PASCAL, you have amazing power: you can write fancy programs more easily in PASCAL than in BASIC because PASCAL helps organize your thinking; and your programs will run faster, too!

American teachers require kids to master LOGO in elementary school, BASIC in high school, and PASCAL in college. Gifted kids are given the opportunity to start BASIC and PASCAL even sooner — and so are kids in progressive schools.

Many high-school seniors take a PASCAL test given by the College Board. Seniors who pass can get "advanced placement" college credit and skip the college’s first year of computer courses.

Quick PASCAL runs on the IBM PC and lists for just $99. Discount dealers sell it for just $42.

If you’re on a tight budget, which should you buy — Quick PASCAL or Turbo PASCAL? Since they’re very similar to each other, you’ll probably buy Quick PASCAL because it costs less. Another advantage of Quick PASCAL is that it lets you edit your programs more easily than Turbo PASCAL. On the other hand, Turbo PASCAL runs your programs faster, consumes less RAM and disk space, comes with instruction manuals that are larger and more thorough, provides on-screen tutorials that are easier to use, understands better commands for advanced programming, and is the standard against which all other versions are judged. (Quick PASCAL was invented just to imitate Turbo PASCAL more cheaply.)

This chapter explains how to use Quick PASCAL and the most common versions of Turbo PASCAL (versions 4, 5.5, and 6).

If you have Turbo PASCAL 7, follow the instructions for Turbo PASCAL 6, which is similar. If you have Turbo PASCAL version 5, follow the instructions for version 5.5.

I’ll comment on how other versions of PASCAL differ.

Copy to the hard disk

Quick PASCAL and Turbo PASCAL come on a pile of floppy disks. You should copy those disks to your hard disk. Here’s how.

The original version of Quick PASCAL comes on five 5¼-inch floppy disks. When you see the C prompt, put the Quick PASCAL Setup/Utilities Disk in drive A and type "a:". The computer will display an A prompt. Type "setup". The computer will say "Microsoft Quick Pascal Setup Program".

Press ENTER twice. The computer will say "Easy Setup Menu". Type the letter I. Press ENTER four times.

Put the Quick PASCAL Program Disk in drive A, and press ENTER. Put the Quick PASCAL Advisor Disk in drive A, and press ENTER. Put the Quick PASCAL Libraries Disk in drive A, and press ENTER. Put the Quick PASCAL Express Disk in drive A; press ENTER twice.

Press R, so that the computer says "Setup Main Menu". Press X, so that you exit to DOS. You’ll see an A prompt.

Turn off the computer, so you can start fresh.

After the C prompt, type "md turbo" (so you’re making a subdirectory called TURBO). After the next C prompt, type "cd turbo" (so you’re changing to the TURBO subdirectory).

Turbo PASCAL 4 comes on three floppy disks. Put one of those disks in drive A, and type "copy a:*.*" (which copies all the floppy’s files onto the hard disk); follow the same procedure for the other two disks.

Turn off the computer, so you can start fresh.

Your Turbo PASCAL comes on four 5¼-inch floppy disks. When you see the C prompt, put the Install/Compiler disk in drive A, and type "a:install". The computer will say "Turbo PASCAL Installation Utility".

Press ENTER four times. You’ll see "C:\TP". Press the BACKSPACE key, then type URBO so you see "C:\TURBO". At the end of the URBO, press ENTER.

Press the F9 key.

If you’re using version 6, put the Turbo Vision/Tour disk in drive A, press ENTER, put the Help disk in drive A, press ENTER, put the BGI/Utilities disk in drive A, and press ENTER twice. (If you’re using version 5.5, put the Tour/Online Help disk in drive A, press ENTER, put the OOP/Demos/BGI/Doc disk in drive A, press ENTER, put the Utilities/Misc disk in drive A, and press ENTER twice.)

You’ll see an A prompt. Turn off the computer, so you can start fresh.

Start PASCAL

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

If you’ve put the DO.BAT file onto your hard disk (as I recommended in the MS-DOS chapter), your life is easy! Just type "do qp" to do Quick PASCAL; type "do turbo" to do Turbo PASCAL.

If you have not put DO.BAT onto your hard disk, your life is harder! You must type "cd qp" and then "qp" to do Quick PASCAL; you must type "cd turbo" and then "turbo" to do Turbo PASCAL.

Press the CAPS LOCK key, so the computer will automatically capitalize everything you type (and your typing will look like the examples in this chapter).

Here’s what to do next.

How to program

For example, type this PASCAL program:

BEGIN;

WRITELN('I WOULD LIKE TO KISS');

WRITELN('YOUR BOTTLE OF WINE');

END.

The program begins with the word BEGIN and ends with the word END. Every line ends with a semicolon, except that the bottom line ends with a period. The middle lines say WRITELN, which tells the computer to WRITE a LiNe.

PROGRAM WINE;

BEGIN;

WRITELN('I WOULD LIKE TO KISS');

WRITELN('YOUR BOTTLE OF WINE');

END.

If you typed the program correctly, the computer will write:

I WOULD LIKE TO KISS

YOUR BOTTLE OF WINE

If you typed the program incorrectly, the computer will say:

Error

(If you’re using Quick PASCAL, then press ENTER.) The computer will put the cursor near your error. Correct the error (by using the arrow keys, DELETE key, and other word-processing keys), then tell the computer to run the program again.

You’ll see the program again. If you wish, edit the program again and run the edited version.

Ancient versions require the top line to say this:

PROGRAM WINE(INPUT,OUTPUT);

Some Apple 2 and Mac versions automatically indent all lines between BEGIN and END and force you to omit the semicolon next to the word BEGIN.

Advanced editing

While typing and editing your program, you can edit faster by using these tricks.…

To delete a whole line, move to that line. Then tap the Y key (which means "Yank it out") while holding down the CONTROL key.

To insert an extra line in the middle of your program, move to where you want the extra line to begin. Press the ENTER key, then the up-arrow.

Here’s how to delete or move a block of text.…

Then say what you want to do to the block. If you want to delete the block, press the DELETE key for Quick PASCAL; press CONTROL with DELETE for Turbo PASCAL 6. If you want to move the block instead, press SHIFT with DELETE, then point where you want the block to appear and press SHIFT with INSERT.

Point at the character after the block’s end. Press CONTROL with K, then press K (which means "klose"). The entire block changes color.

Then say what you want to do to the block. If you want to delete the block, press CONTROL K then Y ("which means "yank"). If you want to move the block instead, point where you want the block to appear and press CONTROL K then V (which means "visible").

Save your program

Here’s how to copy your program onto the hard disk.

Switch programs

Here’s how to switch to other programs.

If you want to invent a new program, say "File New" (by typing FN). If instead you want to retrieve a saved program, do this: say "File Open" (by typing FO), type the program’s name (such as WINE), and press ENTER.

If the computer asks "Save?", press N.

If you want to invent a new program, press F10 then type FN (which means File New). If instead you want to retrieve a saved program, do this: press F3 and ENTER; point at the program you want to use (by using the arrow keys) and press ENTER.

Multiple writing

This program belongs in your bathroom:

BEGIN;

WRITELN('FAR','TIN','G');

END.

The computer will write FAR, TIN, and G all on the same line, like this:

FARTING

Exit

When you finish using PASCAL, here’s how to return to the DOS prompt.

If you’re using a fancy color monitor (such as VGA), you’ll discover that Quick PASCAL has changed the monitor’s colors. To reset the colors, turn the computer off and then back on.

EXE files

When you tell the computer to run the WINE.PAS program, the computer translates it to machine language. The machine-language version (the object code) is called "WINE.EXE". The ".EXE" means "executable object code written in machine language".

If you’re using Quick PASCAL, the computer automatically puts WINE.EXE in your disk’s PASCAL subdirectory. If you’re using Turbo PASCAL instead, the computer puts WINE.EXE in the RAM but not on disk — unless you give a special "Destination Disk" command.

After the computer has run your program and put WINE.EXE on disk, you can run the WINE.EXE machine-language program without using PASCAL. Here’s how: quit PASCAL, then do a "cd" to the PASCAL subdirectory, then type "wine".

Step 1: type a PASCAL program.

Math

PASCAL distinguishes between integers and real numbers. Here’s how PASCAL defines them.…

Integers

An integer contains no decimal point and no exponent.

-27 -27.0 An integer contains no decimal point.

50000 5E4 An integer contains no exponent.

Real numbers

A real number contains a decimal point or the letter E. For example, it can be 0.37 or 5.0 or 6E24. If it contains a decimal point, you should put digits before and after the decimal point.

0.37 .37

5.0 5.

Arithmetic

Like BASIC, PASCAL lets you do arithmetic by using the symbols +, -, *, and /.

If you combine real numbers, the answer is real:

4.9+2.1 is the real number 7.0 (not 7)

5.0-5.0 is the real number 0.0 (not 0)

If you combine a real with an integer, the answer is still real:

3.5*2 is the real number 7.0 (not 7)

3/.5 is the real number 6.0 (not 6)

If you combine integers, the answer is an integer, except for division:

7+4 is the integer 11

7-4 is the integer 3

7*4 is the integer 28

7/4 is the real number 1.75

This program makes the computer do all that arithmetic:

BEGIN;

WRITELN(7+4);

WRITELN(7-4);

WRITELN(7*4);

WRITELN(7/4);

END.

The computer will write:

11

3

28

1.7500000000E+00

(Quick PASCAL writes extra zeros, like this: 1.75000000000000E+0000.)

Let’s try writing all those numbers on the same line:

BEGIN;

WRITELN(7+4,7-4,7*4,7/4);

END.

The computer will write:

11328 1.7500000000E+00

Like BASIC, PASCAL lets you use parentheses to indicate order of operations.

Some versions of PASCAL write 1.75 instead of 1.7500000000E+00. Some Apple 2 and Mac versions automatically round the answer and write 1.8e+0.

Functions

PASCAL lets you use these functions:

ABS(-6) the absolute value of -6; it’s 6

SQR(3) the square of 3; it’s 9

SQRT(9) the square root of 9; it’s 3.0

SIN(2) the sine of 2 radians

COS(2) the cosine of 2 radians

ARCTAN(2) the arctangent of 2, in radians

EXP(5) e5, where e is 2.71828182845904523536

LN(9) the natural logarithm of 9; it’s loge 9

The number in parentheses can be either an integer or a real. The computer’s answer is usually a real (exception: for ABS and SQR, the computer’s answer is an integer if the number in parentheses is an integer).

For example, this program computes the square root of 9:

BEGIN;

WRITELN(SQRT(9));

END.

The computer will write:

3.0000000000E+00

Don’t confuse SQR with SQRT. The SQR means square; the SQRT means square root. To find the square of 3, say SQR(3) or 3*3. In BASIC, you could say 3^2; but in PASCAL, you can’t use the symbol ^; use SQR instead.

To turn a real number into an integer, use these functions:

ROUND(3.9) 3.9 rounded to the nearest integer; it’s 4

TRUNC(3.9) 3.9 truncated (by deleting the .9); it’s 3

If you’re using UCSD PASCAL on an Apple and want to use the functions SQRT, SIN, COS, ATAN, EXP, and LN, you must insert this line immediately under the line that says PROGRAM:

USES TRANSCEND;

Simple variables

You can use variables:

The top line says VAR. The word VAR doesn’t have a semicolon after it; the lines underneath VAR are indented. The indentation is optional but a good habit. To indent easily, tap the TAB key.

For Quick PASCAL, the TAB key indents 8 spaces. For Turbo PASCAL, the TAB key indents just enough to get past the word above (VAR).

On the indented lines, say which variables are integers and which are reals.

Once you’ve indented a line, the computer automatically indents all the lines underneath it. If the computer automatically indents a line that you don’t want to indent, here’s how to undo the indentation: for Turbo PASCAL 5.5, press the BACKSPACE key once; for Turbo PASCAL 4, press the left-arrow key several times; for Quick PASCAL, tap the TAB key while holding down the SHIFT key.

In PASCAL, a variable’s name can be as long as you like: the name can be FRED or WASHINGTON or even SUPERCALIFRAGILISTICEXPIALIDOCIOUS. The name can consists of letters and digits, but must begin with a letter.

In PASCAL, you must put a colon in front of the equal sign.…

FRED:=2; FRED=2;

If you want to add a line saying PROGRAM WINE, put that line above the VAR line.

You can’t set an integer variable equal to a real. For example, if you say —

VAR

ANN: REAL;

BILL: INTEGER;

BEGIN;

ANN:=3.9;

you cannot then say:

BILL:=ANN;

Instead, you must say —

BILL:=ROUND(ANN);

or

BILL:=TRUNC(ANN);

Old versions of PASCAL examine just the first 8 characters of a variable’s name and ignore the rest of the name.

READLN

Instead of saying INPUT, PASCAL says READLN.

VAR

X: REAL;

BEGIN;

WRITELN('WHAT IS YOUR FAVORITE NUMBER?');

READLN(X);

WRITELN('ITS SQUARE ROOT IS',SQRT(X);

END.

When you run the program, the computer asks:

WHAT IS YOUR FAVORITE NUMBER?

Then the READLN(X) statement makes the computer wait for you to input a value of X. The computer expects you to input a real number; if you input an integer instead, the computer will automatically turn it into a real. For example, if you input 9, the computer will automatically turn it into 9.0 and will write:

ITS SQUARE ROOT IS 3.0000000000E+00

IF

The computer can criticize your age:

VAR

AGE: INTEGER;

BEGIN;

WRITELN('HOW OLD ARE YOU?');

READLN(AGE);

IF AGE<18 THEN

BEGIN;

WRITELN('YOU ARE STILL A MINOR.');

WRITELN('AH, THE JOYS OF YOUTH!');

END;

WRITELN('GLAD TO MEET YOU.');

END.

That program makes the computer ask:

HOW OLD ARE YOU?

If you input a number less than 18, the computer replies:

YOU ARE STILL A MINOR.

AH, THE JOYS OF YOUTH!

GLAD TO MEET YOU.

If you input a number that’s at least 18, the computer says just this:

GLAD TO MEET YOU.

In that program, the line that says "IF" is a heading (the lines underneath it are indented), so do not put a semicolon at the end of that line!

ELSE

To make your program fancier, insert the shaded lines:

VAR

AGE: INTEGER;

BEGIN;

WRITELN('HOW OLD ARE YOU');

READ(AGE);

IF AGE<18 THEN

BEGIN;

WRITELN('YOU ARE STILL A MINOR.');

WRITELN('AH, THE JOYS OF YOUTH!');

END

ELSE

BEGIN;

WRITELN('I AM GLAD TO HEAR YOU ARE AN ADULT!');

WRITELN('NOW WE CAN HAVE SOME ADULT FUN!');

END;

WRITELN('GLAD TO MEET YOU.');

END.

If your age is less than 18, the computer will say:

YOU ARE STILL A MINOR.

AH, THE JOYS OF YOUTH!

GLAD TO MEET YOU.

If your age is not less than 18, the computer will say:

GLAD TO HEAR YOU ARE AN ADULT!

NOW WE CAN HAVE SOME ADULT FUN!

GLAD TO MEET YOU.

In that program, the line that says "ELSE" is a heading, so do not put a semicolon after the "ELSE". Immediately above the word ELSE, you’ll see the word END; do not put a semicolon after that END.

Symbols

Like BASIC, PASCAL uses these symbols in the IF line:

< > = <= >= <> AND OR

In the IF line, the symbol for "equals" is "="; outside the IF line, the symbol for "equals" is ":=".

Instead of saying —

IF I=3 OR I=8 OR I=25 OR I=95 THEN

you can say:

IF I IN [3,8,25,95] THEN

That means "If I is in this set of numbers — 3,8,25,95 — then…"

Loops

To create a loop, say FOR or REPEAT or WHILE. Here’s how to use those words.

FOR

Like BASIC, PASCAL uses the word FOR. This program makes the computer get drunk:

VAR

I: INTEGER;

BEGIN;

FOR I := 7 TO 10 DO

BEGIN;

WRITELN('I DRANK ',I,' BOTTLES OF BEER');

WRITELN('HOORAY!');

END;

WRITELN('NOW I AM DEAD DRUNK');

END.

Since the FOR line is a heading, do not put a semicolon at the end of it. When you run the program, the computer will write:

I DRANK 7 BOTTLES OF BEER

HOORAY!

I DRANK 8 BOTTLES OF BEER

HOORAY!

I DRANK 9 BOTTLES OF BEER

HOORAY!

I DRANK 10 BOTTLES OF BEER

HOORAY!

NOW I AM DEAD DRUNK

If you want the computer to count backwards — from 10 down to 7 — change the FOR line to this:

FOR I := 10 DOWNTO 7 DO

REPEAT

This program plays a guessing game:

VAR

GUESS: INTEGER;

BEGIN;

WRITELN('I AM THINKING OF A NUMBER FROM 1 TO 10');

REPEAT

WRITELN('YOU HAVE NOT GUESSED MY NUMBER YET');

WRITELN('WHAT IS MY NUMBER?');

READLN(GUESS);

UNTIL GUESS=6;

WRITELN('CONGRATULATIONS! YOU GUESSED IT! MY NUMBER IS 6');

END.

The computer begins the game by saying:

I AM THINKING OF A NUMBER FROM 1 TO 10

Then the computer REPEATs the following procedure several times: it says YOU HAVE NOT GUESSED MY NUMBER YET, asks WHAT IS MY NUMBER, waits for the human to input a guess, and checks whether the human guessed 6. It repeats that procedure again and again, UNTIL the human finally guesses 6. Then the computer says:

CONGRATULATIONS! YOU GUESSED IT! MY NUMBER IS 6

In that program, the computer REPEATs the indented lines, UNTIL GUESS is 6.

If a program contains the word REPEAT, it must also contain the word UNTIL. The lines between REPEAT and UNTIL are done repeatedly. After each time, the computer checks whether to repeat again.

Since the REPEAT line’s a heading, it has no semicolon.

Like an IF line, the UNTIL line can contain these symbols:

< > = <= >= <> AND OR IN

Here’s another example. Let’s make the computer start with the number 3 and keep doubling it, like this:

3

6

12

24

etc.

Let’s make the computer keep doubling but not go over 1000. So altogether, let’s make the computer write:

3

6

12

24

48

96

192

384

768

THOSE ARE ALL THE NUMBERS BELOW 1000

Here’s the program:

VAR

I: INTEGER;

BEGIN;

WRITELN(I);

I:=I*2;

UNTIL I>=1000;

WRITELN('THOSE ARE ALL THE NUMBERS BELOW 1000');

END.

WHILE

The word WHILE resembles the word REPEAT. For example, the previous program (which doubled 3 repeatedly) can be rewritten to use WHILE:

VAR

I: INTEGER;

BEGIN;

WRITELN(I);

I:=I*2;

END;

WRITELN('THOSE ARE ALL THE NUMBERS BELOW 1000');

END.

The indented lines say to WRITELN(I) and then double I. The computer repeats those indented lines many times. Before each repetition, the computer checks to make sure I is still below 1000. When I passes 1000, the computer stops looping and proceeds to the next line, which writes THOSE ARE ALL THE NUMBERS BELOW 1000.

These two structures resemble each other:

REPEAT WHILE I<1000 DO

END;

Each of those structures makes the computer repeat the indented lines and check whether I is still below 1000. If you say REPEAT, the check is done at the loop’s bottom, so the computer goes through the loop once before checking. If you say WHILE, the check is done at the loop’s top, so the computer checks whether I<1000 before doing the loop the first time.

Logic tricks

Every statement must end with a semicolon. You can put several statements on the same line:

A:=3; A:=3; B:=7.6; WRITELN(A+B);

B:=7.6;

WRITELN(A+B);

You can continue a statement on the next line:

A:=5-2+1; A:=

5-2

+1;

But do not divide a statement in the middle of a word, number, symbol, or string:

IF AGE>=18 THEN IF AGE IF AG IF AGE>=1 IF AG>

>=18 THEN E>=18 THEN 8 THEN =18 THEN

Omitting semicolons

You can omit the semicolon after BEGIN:

BEGIN; BEGIN

You can omit a semicolon, if the next word is END:

A:=3; A:=3

END; END;

You can omit a semicolon, if the next word is UNTIL:

I=*2; I=I*2

UNTIL I>=1000; UNTIL I>=1000;

Omitting BEGIN and END

If a heading heads just one indented line (besides BEGIN and END), you can put that indented line next to the heading (and omit the BEGIN and END).

FOR I := 1 TO 9 DO FOR I := 1 TO 9 DO WRITELN(I);

BEGIN;

WRITELN(I);

END;

WHILE A<100 DO WHILE A<100 DO A:=A+7;

BEGIN;

A=A+7;

END;

IF AGE>=65 THEN IF AGE>=65 THEN WRITELN('OLD');

BEGIN;

WRITELN('OLD');

END;

IF WEIGHT>220 THEN IF WEIGHT>220 THEN WRITELN('FAT') ELSE WRITELN('OKAY');

BEGIN;

WRITELN('FAT');

END

ELSE

BEGIN;

WRITELN('OKAY');

END;

REPEAT REPEAT A:=A+7 UNTIL A>100;

A:=A+7;

UNTIL A>100;

Comments

To put comments into your program, surround the comment by braces:

10 'I HATE COMPUTERS {I HATE COMPUTERS}

Do not put a semicolon after the comment.

If your screen can display colors, Quick PASCAL makes the comments and braces turn green.

(*I HATE COMPUTERS*)

GOTO

You can say GOTO:

LABEL 10;

BEGIN;

WRITELN('MY DOG');

GOTO 10;

WRITELN('NEVER');

10: WRITELN('DRINKS WHISKEY');

END.

The top line warns the computer that a future line will be labeled "line 10". The rest of the program makes the computer write MY DOG, then skip to line 10, which makes the computer write DRINKS WHISKEY. Altogether, the computer will write:

MY DOG

DRINKS WHISKEY

Do not put a space between GO and TO.

Here’s another example:

LABEL 10;

BEGIN;

10: WRITELN('LOVE');

WRITELN('HATE');

GOTO 10;

END.

The computer will write LOVE and HATE repeatedly:

LOVE

HATE

LOVE

HATE

LOVE

HATE

etc.

To abort the program, tap the C key while holding down the CONTROL key. (For Quick PASCAL, then press ENTER.)

If your program contains lines numbered 10, 20, and 100, put this statement at the top of your program:

LABEL 10,20,100;

Put that statement at the very top of your program: the only statement that should go above it is the one saying PROGRAM. The PROGRAM and LABEL lines go above all other lines — even above VAR and BEGIN.

Each line number must be small: no higher than 9999.

In PASCAL, you’ll rarely need to say GOTO. Instead, try using the words IF, ELSE, FOR, REPEAT, and WHILE.

(*$G+*)

PROGRAM SKIPPER;

LABEL 10;

etc.

Procedures

This program teases you, with the help of some insults:

PROCEDURE INSULT;

BEGIN;

WRITELN('YOU ARE STUPID');

WRITELN('YOU ARE UGLY');

END;

{MAIN ROUTINE}

BEGIN;

WRITELN('WE ALL KNOW...');

INSULT;

WRITELN('...AND YET WE LOVE YOU');

END.

That program begins by defining INSULT to be this procedure:

WRITELN('YOU ARE STUPID');

WRITELN('YOU ARE UGLY');

The main routine makes the computer write ‘WE ALL KNOW...’, then do the INSULT procedure, then write ‘...AND YET WE LOVE YOU’; altogether, the computer will write:

WE ALL KNOW...

YOU ARE STUPID

YOU ARE UGLY

...AND YET WE LOVE YOU

The PROCEDURE, called INSULT, is a subroutine. In PASCAL, subroutines come before the main routine. (In BASIC, subroutines come after the main routine instead.)

Put a program’s VAR above any procedures:

BEGIN;

END;

BEGIN;

END.

Advanced variables

You’ve seen that a variable can stand for a number. This section explains how to make a variable stand for a character, array, or string.

CHAR

A variable can stand for a character:

VAR

BEGIN;

END.

The computer will write U and P like this:

UP

You can put a character variable after the word FOR:

VAR

I: CHAR;

BEGIN;

FOR I := 'A' TO 'E' DO WRITELN(I);

END.

The computer will write:

A

B

C

D

E

ARRAY

Let’s make X be this list of real numbers: 4.2, 71.6, 8.3, 92.6, 403.7, 1.4. Here’s how:

VAR

X: ARRAY [1..6] OF REAL;

BEGIN;

X[1]:=4.2;

X[2]:=71.6;

X[3]:=8.3;

X[4]:=92.6;

X[5]:=403.7;

X[6]:=1.4;

WRITELN(X[1]+X[2]+X[3]+X[4]+X[5]+X[6]);

END.

The computer will write the sum, 581.8.

Subscripts can be negative:

VAR

Y: ARRAY [-2..3] OF REAL;

BEGIN;

Y[-2]:=400.1;

Y[-1]:=274.1;

Y[0]:=9.2;

Y[1]:=8.04;

Y[2]:=0.6;

Y[3]:=-5.0;

WRITELN(Y[-2]+Y[-1]+Y[0]+Y[1]+Y[2]+Y[3]);

END.

The computer will write the sum, 687.04.

Here’s how to make Z be a table having 6 rows and 4 columns of reals:

VAR

Z: ARRAY [1..6, 1..4] OF REAL;

The number in the 3rd row and 2nd column is called Z[3,2]. The entire first row of Z is called Z[1]; the second row is called Z[2]; etc. For example, if you say —

Z[5]:=Z[3];

the computer will look at the real numbers in the 3rd row of Z, and copy them into the 5th row. Suppose W is another array that has 6 rows and 4 columns; if you say —

W:=Z;

the computer will look at each real number in Z and copy it into W.

You can have many kinds of arrays: you can have an array of REAL, an array of INTEGER, and even an array of CHAR.

STRING

A variable can stand for a string:

VAR

X: STRING;

BEGIN;

X:='I LOVE MY MOTH';

WRITELN(X,'ER');

END.

The computer will write `I LOVE MY MOTH’ and then `ER’, like this:

I LOVE MY MOTHER

You can make the computer read a string:

VAR

X: STRING;

BEGIN;

WRITELN('WHAT IS YOUR NAME?');

READLN(X);

WRITELN('HELLO ',X,' THE BEAUTIFUL');

END.

When you run that program, the computer asks:

WHAT IS YOUR NAME?

Then the READLN(X) statement makes the computer wait for you to input a string. If you input the name MARILYN MONROE, the computer will write:

HELLO MARILYN MONROE THE BEAUTIFUL

The oldest versions of PASCAL require you to say PACKED ARRAY [1..80] OF CHAR instead. Some of those old versions can’t read or write the whole array string at once: instead you must create FOR loops that read and write one character at a time.