Section 4.14. Loops Within Loops

4.14. Loops Within Loops

You can nest loops as you see fit, like this:

     for ($i = 1; $i < 3; $i = $i + 1) {             for ($j = 1; $j < 3; $j = $j + 1) {                     for ($k = 1; $k < 3; $k = $k + 1) {                             print "I: $i, J: $j, K: $k\n";                     }             }     }

Here's the output:

     I: 1, J: 1, K: 1     I: 1, J: 1, K: 2     I: 1, J: 2, K: 1     I: 1, J: 2, K: 2     I: 2, J: 1, K: 1     I: 2, J: 1, K: 2     I: 2, J: 2, K: 1     I: 2, J: 2, K: 2

In this situation, using break is a little more complicated, as it only exits the containing loop. For example:

     for ($i = 1; $i < 3; $i = $i + 1) {             for ($j = 1; $j < 3; $j = $j + 1) {                     for ($k = 1; $k < 3; $k = $k + 1) {                             print "I: $i, J: $j, K: $k\n";                             break;                     }             }     }

This time the script will print out the following:

     I: 1, J: 1, K: 1     I: 1, J: 2, K: 1     I: 2, J: 1, K: 1     I: 2, J: 2, K: 1

As you can see, the $k loop only loops once because of the break call. However, the other loops execute several times. You can exercise even more control by specifying a number after break, such as break 2, to break out of two loops or switch/case statements. For example:

     for ($i = 1; $i < 3; $i = $i + 1) {             for ($j = 1; $j < 3; $j = $j + 1) {                     for ($k = 1; $k < 3; $k = $k + 1) {                             print "I: $i, J: $j, K: $k\n";                             break 2;                     }             }     }

That outputs the following:

     I: 1, J: 1, K: 1     I: 2, J: 1, K: 1

This time the loop only executes twice, because the $k loop calls break 2, which breaks out of the $k loop and out of the $j loop, so only the $i loop will go around again. This could even be break 3, meaning break out of all three loops and continue normally.

The break command applies to both loops and switch/case statements. For example:

     for ($i = 1; $i < 3; $i = $i + 1) {             for ($j = 1; $j < 3; $j = $j + 1) {                     for ($k = 1; $k < 3; $k = $k + 1) {                             switch($k) {                                     case 1:                                             print "I: $i, J: $j, K: $k\n";                                             break 2;                                     case 2:                                             print "I: $i, J: $j, K: $k\n";                                             break 3;                             }                     }             }     }

The break 2 line will break out of the switch/case block and also out of the $k loop, whereas the break 3 line will break out of those two and also the $j loop. To break out of the loops entirely from within the switch/case statement, break 4 is required.