Difference between revisions of "While"

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(undo revision 025DCC by Paskal (talk): this content is rather presented on Continue and, by the way, the example is imaginably poorly designed)
Tag: Undo
 
Line 33: Line 33:
 
end;
 
end;
 
end.
 
end.
</syntaxhighlight>
 
 
 
 
You can use <syntaxhighlight lang="pascal" inline>Continue</syntaxhighlight> to jump to the end of the loop.
 
In the example below all values from 1 to 10 are printed, except 5.
 
<syntaxhighlight lang="pascal" line highlight="9">
 
program whileDemo(input, output, stderr);
 
var
 
  i:integer=0;
 
begin
 
  while true do
 
  begin
 
    inc(i);
 
    if i>10 then break;
 
    if i=5 then continue;
 
    writeLn(i);
 
  end;
 
end; 
 
 
</syntaxhighlight>
 
</syntaxhighlight>
  

Latest revision as of 05:22, 25 January 2023

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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 statement is executed. This is the main difference to a repeat  until-loop, where the loop body 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 statement 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: begindoelseendforifrepeatthenuntilwhile