Difference between revisions of "While"
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<syntaxhighlight lang="pascal" enclose="none">while</syntaxhighlight> in conjunction with [[Do|<syntaxhighlight lang="pascal" enclose="none">do</syntaxhighlight>]] repeats a statement as long as a condition evaluates to [[True|<syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>]]. | <syntaxhighlight lang="pascal" enclose="none">while</syntaxhighlight> in conjunction with [[Do|<syntaxhighlight lang="pascal" enclose="none">do</syntaxhighlight>]] repeats a statement as long as a condition evaluates to [[True|<syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>]]. | ||
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* [[Infinite loop]] | * [[Infinite loop]] | ||
{{Keywords}} | {{Keywords}} | ||
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Revision as of 10:55, 4 March 2020
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Back to Reserved words.
while
in conjunction with do
repeats a statement as long as a condition evaluates to true
.
The condition expression is evaluated prior each iteration, determining whether the following block (or single statement) is executed.
This is the main difference to a repeat … until
-loop, where the block is executed at any rate, but succeeding iterations do not necessarily happen, though.
The following example contains unreachable code:
1program whileFalse(input, output, stderr);
2
3begin
4 while false do
5 begin
6 writeLn('never gets printed');
7 end;
8end.
You usually use while
-loops where, in contrast to for
-loops, a running index variable is not required, the block executed can't be deduced from an index that's incremented by one, or to avoid a break
-statement (which usually indicates bad programming style).
1program whileDemo(input, output, stderr);
2
3var
4 x: integer;
5begin
6 x := 1;
7
8 // prints non-negative integer powers of two
9 while x < high(x) div 2 do
10 begin
11 writeLn(x);
12 inc(x, x); // x := x + x
13 end;
14end.
See also
Keywords: begin — do — else — end — for — if — repeat — then — until — while