Руководство по PHP
Пред. | 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`