Web Database Applications with PHP and MySQL, 2nd Edition

Loops

Loops add control to scripts so that statements can be repeatedly executed as long as a conditional expression remains true. There are four loop statements in PHP: while, do...while, for, and foreach. The first three are general-purpose loop constructs, while the foreach is used exclusively with arrays and is discussed in the next chapter.

while

The while loop is the simplest looping structure but sometimes the least compact to use. The while loop repeats one or more statements—the loop body—as long as a condition remains true. The condition is checked first, then the loop body is executed. So, the loop never executes if the condition isn't initially true. Just as with the if statement, more than one statement can be placed in braces to form the loop body.

The following fragment illustrates the while statement by printing out the integers from 1 to 10 separated by a space character:

$counter = 1;
while ($counter < 11)
{
    print $counter . " ";
    $counter++;
}

do...while

The difference between while and do...while is the point at which the condition is checked. In do...while, the condition is checked after the loop body is executed. As long as the condition remains true, the loop body is repeated.

You can emulate the functionality of the previous while example as follows:

$counter = 1;
do
{
    print $counter . " ";
    $counter++;
} while ($counter < 11);

The contrast between while and do...while can be seen in the following example:

$counter = 100; do { print $counter . " "; $counter++; } while ...