Difference between revisions of "While"
m (ordinal numbers in syntaxhighlight) |
|||
| Line 3: | Line 3: | ||
<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>]]. | ||
The condition expression is evaluated prior each iteration, determining whether the following block (or single statement) is executed. | 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|<syntaxhighlight lang="pascal" enclose="none">repeat … until</syntaxhighlight>-loop]], where the block is executed at any rate, but succeeding iterations do not necessarily happen, though. | + | This is the main difference to a [[Repeat|<syntaxhighlight lang="pascal" enclose="none">repeat … until</syntaxhighlight>-loop]], where the [[Block|block]] is executed at any rate, but succeeding iterations do not necessarily happen, though. |
The following example contains unreachable code: | The following example contains unreachable code: | ||
| Line 17: | Line 17: | ||
</syntaxhighlight> | </syntaxhighlight> | ||
| − | You usually use <syntaxhighlight lang="pascal" enclose="none">while</syntaxhighlight>-loops where, in contrast to [[For|<syntaxhighlight lang="pascal" enclose="none">for</syntaxhighlight>-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|<syntaxhighlight lang="pascal" enclose="none">break</syntaxhighlight>-statement]] (which usually indicates bad programming style). | + | You usually use <syntaxhighlight lang="pascal" enclose="none">while</syntaxhighlight>-loops where, in contrast to [[For|<syntaxhighlight lang="pascal" enclose="none">for</syntaxhighlight>-loops]], a running index [[Variable|variable]] is not required, the block executed can't be deduced from an index that's incremented by one, or to avoid a [[Break|<syntaxhighlight lang="pascal" enclose="none">break</syntaxhighlight>-statement]] (which usually indicates bad programming style). |
<syntaxhighlight lang="pascal" line highlight="9"> | <syntaxhighlight lang="pascal" line highlight="9"> | ||
program whileDemo(input, output, stderr); | program whileDemo(input, output, stderr); | ||
Revision as of 20:35, 10 January 2019
│
Deutsch (de) │
English (en) │
suomi (fi) │
français (fr) │
русский (ru) │
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
