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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 the numbers 1 through 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;