一、问题
先看一个例子：

<?php
$ar = array(1, 2, 3);
var_dump($ar);
foreach ($ar as &$v) {}
foreach ($ar as $v) {}
var_dump($ar);
?>

<?php 
//声明一个三维数组 
$info=array( 
"user"=>array( 
array(1,"zhangsan",20,"nan"), 
array(2,"lisi",20,"nan"), 
array(3,"wangwu",25,"nv")