PHP. Руководство по PHP. 2005

for

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.

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; $i <= 10; 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;

do-while

foreach

Отвечу на любые вопросы. С уважением, Дмитрий Владимирович.

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