Commodore 128D - Introduction; Until

Introduction
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Advanced
Looping
This section introduces you to some powerful BASIC commands and
statements that you probably haven't seen before, even if you are an
experienced BASIC programmer. If you're familiar with programming
in BASIC, you've probably encountered many situations in which you
could have used these commands and statements. This section
explains the concepts behind each command and gives examples of
how to use each command in a program. (A complete list and an
explanation of these commands and statements may be found in
Chapter V, BASIC 7.0 Encyclopedia.) This section also describes how
to use the special keys that are available to you in C128 mode.
The DOf LOOP Statement
The DO/LOOP statement provides more sophisticated ways to cre
ate a loop than do the GOTO, GOSUB or FOR/NEXT statements. The
DO/LOOP statement combination brings to the BASIC language a
very powerful and versatile technique normally available only in
structured programming languages. We'll discuss just a few possible
uses of DO/LOOP in this explanation.
If you want to create an infinite loop, you start with a DO statement,
then enter the line or lines that specify the action you want the com
puter to perform. Then end with a LOOP statement, like this:
100 DO
110 PRINT "REPETITION"
120 LOOP
Press the RUN/STOP key to stop the program.
The directions following the DO statement are carried out until the
program reaches the LOOP statement (line 120); control is then
transferred back to the DO statement (line 1OO)< Thus, whatever
statements are in between DO and LOOP are performed indefinitely.
UNTIL Another useful technique is to combine the DO/
LOOP with the UNTIL statement. The UNTIL
statement sets up a condition that directs the
loop. The loop will run continually unless the
condition for UNTIL happens.
100 DO:
110 : INPUT "DO YOU LIKE YOUR COMPUTER";A$
120 LOOP UNTIL A$ = "YES"
130 PRINT "THANK YOU"
USING C128 MODE—Some BASIC Commands and Keyboard Operations Unique to
75 C128 Mode