初学者问个简单的逻辑有关问题，求解答

菜鸟问个简单的逻辑问题，求解答
我是想实现62进制的功能，可是下面这段代码只能echo出来，不能返回，不知道是什么原因，求高手解答

<br />function dwz($id,$str=""){<br />	$a=array("0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z");<br />	$zs=(int)($id/sizeof($a));<br />	$xs=$id%sizeof($a);<br />	if($zs>=sizeof($a)){<br />		$str=$a[$xs].$str;<br />		dwz($zs,$str);<br />	}<br />	else{<br />		if($str==""){<br />			return $a[$zs].$a[$xs];<br />		}<br />		else{<br />			echo   $a[$zs].$str;//这里只能输出<br />			return $a[$zs].$str;//返回没值，不知道什么原因<br />		}<br />	}<br />}<br />for($i=999990;$i<=1000000;$i++){<br />	echo dwz($i);<br />	echo "<br>";<br />}<br />

逻辑 菜鸟 简单的

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------解决方案--------------------
第7行 dwz($zs,$str);
没有承接返回
$str = dwz($zs,$str);

函数结束处还需要有 return $str;

------解决方案--------------------

<br />    if($zs>=sizeof($a)){<br />         $str=$a[$xs].$str;<br />         dwz($zs,$str); //这里加入return： return dwz($zs, $str);    <br />}<br />