While
│
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