Руководство по PHP
Пред. | Глава 16. Control Structures | След.

# `for`

`for` loops are the most complex loops in PHP. They behave like their C counterparts. The syntax of a `for` loop is:

    for (expr1; expr2; expr3)
        statement

The first expression (`expr1`) is evaluated (executed) once unconditionally at the beginning of the loop.

In the beginning of each iteration, `expr2` is evaluated. If it evaluates to `TRUE`, the loop continues and the nested statement(s) are executed. If it evaluates to `FALSE`, the execution of the loop ends.

At the end of each iteration, `expr3` is evaluated (executed).

Each of the expressions can be empty or contain multiple expressions separated by commas. Comma separated expressions in expr2 are treated similarly to being separated by the || operator but has a lower precedence than ||. `expr2` being empty means the loop should be run indefinitely (PHP implicitly considers it as `TRUE`, like C). This may not be as useless as you might think, since often you'd want to end the loop using a conditional `break` statement instead of using the `for` truth expression.

Consider the following examples. All of them display numbers from 1 to 10:

`<?php /* example 1 */ for ($i = 1; $i <= 10; $i++) { echo $i; } /* example 2 */ for ($i = 1; ; $i++) { if ($i > 10) { break; } echo $i; } /* example 3 */ $i = 1; for (; ; ) { if ($i > 10) { break; } echo $i; $i++; } /* example 4 */ for ($i = 1, $j = 0; $i <= 10; $j += $i, print $i, $i++); ?>`

Of course, the first example appears to be the nicest one (or perhaps the fourth), but you may find that being able to use empty expressions in `for` loops comes in handy in many occasions.

PHP also supports the alternate "colon syntax" for `for` loops.

    for (expr1; expr2; expr3):
        statement
        ...
    endfor;

Пред. | Начало | След.
`do-while` | Уровень выше | `foreach`