foreach

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# `foreach`

PHP 4 (not PHP 3) includes a `foreach` construct, much like Perl and some other languages. This simply gives an easy way to iterate over arrays. `foreach` works only on arrays, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variables. There are two syntaxes; the second is a minor but useful extension of the first:

    foreach(array_expression as $value) statement
    foreach(array_expression as $key => $value) statement

The first form loops over the array given by `array_expression`. On each loop, the value of the current element is assigned to `$value` and the internal array pointer is advanced by one (so on the next loop, you'll be looking at the next element).

The second form does the same thing, except that the current element's key will be assigned to the variable `$key` on each loop.

> Note: When `foreach` first starts executing, the internal array pointer is automatically reset to the first element of the array. This means that you do not need to call reset() before a `foreach` loop.

> Note: Also note that `foreach` operates on a copy of the specified array, not the array itself, therefore the array pointer is not modified as with the each() construct and changes to the array element returned are not reflected in the original array.

> Note: `foreach` does not support the ability to suppress error messages using '@'.

You may have noticed that the following are functionally identical:

    reset ($arr);
    while (list(, $value) = each ($arr)) {
        echo "Value: $value<br>\n";
    }

    foreach ($arr as $value) {
        echo "Value: $value<br>\n";
    }

The following are also functionally identical:

    reset ($arr);
    while (list($key, $value) = each ($arr)) {
        echo "Key: $key; Value: $value<br>\n";
    }

    foreach ($arr as $key => $value) {
        echo "Key: $key; Value: $value<br>\n";
    }

Some more examples to demonstrate usages:

    /* foreach example 1: value only */

    $a = array (1, 2, 3, 17);

    foreach ($a as $v) {
       print "Current value of \$a: $v.\n";
    }

    /* foreach example 2: value (with key printed for illustration) */

    $a = array (1, 2, 3, 17);

    $i = 0; /* for illustrative purposes only */

    foreach($a as $v) {
        print "\$a[$i] => $v.\n";
        $i++;
    }

    /* foreach example 3: key and value */

    $a = array (
        "one" => 1,
        "two" => 2,
        "three" => 3,
        "seventeen" => 17
    );

    foreach($a as $k => $v) {
        print "\$a[$k] => $v.\n";
    }

    /* foreach example 4: multi-dimensional arrays */

    $a[0][0] = "a";
    $a[0][1] = "b";
    $a[1][0] = "y";
    $a[1][1] = "z";

    foreach($a as $v1) {
        foreach ($v1 as $v2) {
            print "$v2\n";
        }
    }

    /* foreach example 5: dynamic arrays */

    foreach(array(1, 2, 3, 4, 5) as $v) {
        print "$v\n";
    }

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