While - Commodore 128 System Manual

directs the loop. The loop will run continually unless the condition
for UNTIL happens.
100 DO: INPUT " DO YOU LIKE YOUR COMPUTER";A$
110 LOOP UNTIL A$="YES"
120 PRINT "THANK YOU"
The DO/LOOP statement is often used to repeat an entire
routine indefinitely in the body of a program, as in the following:
10 PRINT " PROGRAM CONTINUES UNTIL YOU TYPE
QUIT'"
20 DO UNTIL A$=" QUIT"
30 INPUT " DEGREES FAHRENHEIT" ;F
40 C =(5/9)*(F-32)
50 PRINT F;" DEGREES FAHRENHEIT EQUALS " ;C; "
DEGREES CELSIUS"
60 INPUT "AGAIN OR QUIT" ;A$
70 LOOP
80 END
Another use of DO/LOOP is as a counter, where the UNTIL
statement is used to specify a certain number of repetitions.
10 N=2*2
20 PRINT"TWO DOUBLED EQUALS" ; N
30 DO UNTIL X=25
40 X=X+1
50 N=N*2
60 PRINT" DOUBLED" ;X+1;"TIMES...";N
70 LOOP
80 END
Notice that if you leave the counter statement out (the UNTIL
X=25 part in line 30), the number is doubled indefinitely until an
OVERFLOW error occurs.

WHILE

The WHILE statement works in a similar way to UNTIL, but the
loop is repeated only while the condition is in effect, such as in
this reworking of the last brief program:
100 DO: INPUT " DO YOU LIKE YOUR COMPUTER";A$
110 LOOP WHILE A $ < > "YES"
120 PRINT "THANK YOU"
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