主从结构的JSON要如何分拆

主从结构的JSON要怎么分拆
$a='{"head":{"id":"4","userno":"12345","username":"CDZ1"},"body":[{"orderno":"1","price":"15.00","qty":"1"},{"orderno":"1","price":"9.00","qty":"1"}]}';

这样的一段jsoin,  我要单独取得head 部分的字段值及body 部份的字段值， 比如取 head 部份的 userno,及 body 部份的 price.
------解决思路----------------------
从这样的数组中都不会取出想要的数据，你的老师该打屁股了

array (<br />  'head' =>   array (<br />    'id' => '4',<br />    'userno' => '12345',<br />    'username' => 'CDZ1',<br />  ),<br />  'body' =>   array (<br />    0 =>     array (<br />      'orderno' => '1',<br />      'price' => '15.00',<br />      'qty' => '1',<br />    ),<br />    1 =>     array (<br />      'orderno' => '1',<br />      'price' => '9.00',<br />      'qty' => '1',<br />    ),<br />  ),<br />)

------解决思路----------------------

<?php <br />@header("Content-type: text/html; charset=utf-8");<br />$a='{"head":{"id":"4","userno":"12345","username":"CDZ1"},"body":[{"orderno":"1","price":"15.00","qty":"1"},{"orderno":"1","price":"9.00","qty":"1"}]}';<br />$obj=json_decode($a);<br />echo 'userno:'.$obj->head->userno;<br />echo '<br/>price:'.$obj->body[0]->price;<br /><br />/////或：<br /><br />echo "<br/><br/><br/>";<br />$ary=json_decode($a,true);<br />echo 'userno:'.$ary['head']['userno'];<br />echo '<br/>price:'.$ary['body'][0]['price'];<br />?>