php index of iteration in foreach code example

Example 1: for each php

<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
    $value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
unset($value); // break the reference with the last element
?>

Example 2: php foreach index

foreach($array as $key=>$value) {
    // do stuff
}