A while statement is similar to a repeat statement, except that the control condition is evaluated before the first execution of the statement sequence. Hence, if the condition is false, the statement sequence is never executed.
The syntax of a while statement is
while expression do statement
where expression returns a Boolean value and statement can be a compound statement. The while statement executes its constituent statement repeatedly, testing expression before each iteration. As long as expression returns True, execution continues.
Examples of while statements include
while Data[I] <> X do I := I + 1;
while I > 0 do
begin
if Odd(I) then Z := Z * X;
I := I div 2;
X := Sqr(X);
end;
while not Eof(InputFile) do
begin
Readln(InputFile, Line);
Process(Line);
end;