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Loops are used for repetition of certain
statements for a set number of times or according to a certain condition.
FOR loop (unconditional loop)
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Repeat instructions for a set number of
times.
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Uses a counter (must be ordinal: integer or
char)
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Uses a start and ending value that determines
repetitions.
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Can count/move up (e.g. 1 TO 10) or down (10
DOWNTO 1).
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Structure:
FOR <counter> := <start value> TO <ending value> DO
BEGIN
<statements;>
END;
WHILE loop (conditional loop)
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Repeats depending on a certain condition(s).
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Repeats while a certain condition is TRUE.
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ITC:
- Variable tested at beginning of loop must have initial value.
- Variable is tested at the beginning of loop.
- Variable must change in order for loop to stop.
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Structure:
WHILE <condition(s)> DO
BEGIN
<statement(s)>
<change condition to stop loop>
END;
REPEAT loop (conditional loop)
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Repeats depending on a certain condition(s).
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Unlike the WHILE loop the REPEAT loop tests
for a condition at the end of executing certain statements rather than before.
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Instructions in a REPEAT loop will always be
executed at least once.
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Does not need a BEGIN and END.
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The condition(s) indicate when to stop not
when to go on as with the WHILE.
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ICT
- Variables to be tested must be initialized before execution.
- Variable must be changed at the end of loop to avoid an infinite loop (loop
will never stop repeating)
- Variable is tested at the end of the loop. If the statement is FALSE then the
loop will be repeated again.
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Structure:
REPEAT
<statement(s)>
<change condition to stop loop>
UNTIL <conditions to stop>;
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