<?php $arr = array(1, 2, 3, 4); foreach ($arr as &$value) { $value = $value * 2; }// $arr is now array(2, 4, 6, 8) // without an unset($value), $value is still a reference to the last item: $arr[3] foreach ($arr as $key => $value) { // $arr[3] will be updated with each value from $arr... echo "{$key} => {$value} "; print_r($arr); }// ...until ultimately the second-to-last value is copied onto the last value // output: // 0 => 2 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 2 ) // 1 => 4 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 4 ) // 2 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 ) // 3 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 ) ?> &是使用到reference 以上轉載於 http://php.net/manual/en/control-structures.foreach.php 我本來看不懂,後來找到了答案→ http://ccckaass.pixnet.net/blog/post/298283101-%5bphp%5d-foreach%E7%9A%84%26%28%E5%8F%83%E7%85%A7%E6%A8%A1%E5%BC%8F