Computer Decisionsthe If-Then Statement - Commodore 128 System Manual

This section describes how to use a number of powerful BASIC
commands, functions and programming techniques that can be
used in both C128 and C64 modes.
These commands and functions allow you to program repeated
actions through looping and nesting techniques; handle tables of
values; branch or jump to another section of a program, and
return from that section; assign varying values to a quantity—and
more. Examples and sample programs show just how these
BASIC concepts work and interact.

COMPUTER DECISIONSTHE IF-THEN STATEMENT

Now that you know how to change the values of variables, the
next step is to have the computer make decisions based on
these updated values. You do this with the IF-THEN statement.
You tell the computer to execute a command only IF a condition
is true (e.g., IF X=5). The command you want the computer to
execute when the condition is true comes after the word THEN in
the statement. Clear your computer's memory by typing NEW and
pressing RETURN, then type in this program:
10 J=0
20 J=J+1
30 ? J,''COMMODORE 128"
40 IF J=5 THEN GOTO 60
50 GOTO 20
60 END
You no longer have to press the STOP key to break out of a
looping program. The IF-THEN statement tells the computer to
keep printing " COMMODORE 128" and incrementing
(increasing) J until J= 5 is true. When an IF condition is false, the
computer jumps to the next line of the program, no matter what
comes after the word THEN.
Notice the END command in line 60. It is good practice to put an
END statement as the last line of your program. It tells the
computer where to stop executing statements.
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