Глава 16. Control Structures

След.

do-while

do-while loops are very similar to

while loops, except the truth expression is

checked at the end of each iteration instead of in the beginning.

The main difference from regular while loops is

that the first iteration of a do-while loop is

guaranteed to run (the truth expression is only checked at the end

of the iteration), whereas it's may not necessarily run with a

regular while loop (the truth expression is

checked at the beginning of each iteration, if it evaluates to

FALSE right from the beginning, the loop

execution would end immediately).

There is just one syntax for do-while loops:

<?php $i = 0; do { echo $i; } while ($i> 0); ?>

The above loop would run one time exactly, since after the first

iteration, when truth expression is checked, it evaluates to

FALSE ($i is not bigger than 0) and the loop

execution ends.

Advanced C users may be familiar with a different usage of the

do-while loop, to allow stopping execution in

the middle of code blocks, by encapsulating them with

do-while (0), and using the break

statement. The following code fragment demonstrates this:

<?php do { if ($i < 5){ echo "i is not big enough"; break; } $i *= $factor; if ($i < $minimum_limit){ break; } echo "i is ok"; /* process i */ } while (0); ?>

Don't worry if you don't understand this right away or at all.

You can code scripts and even powerful scripts without using this

'feature'.

Пред.

Начало

След.

while

Уровень выше

for

Отвечу на любые вопросы. С уважением, Дмитрий Владимирович.

Ваше письмо	×

⇪