<?php

/**

  *php递归函数细节

  *从1到5的阶乘

* */

header("Content-Type:text/html;charset=utf-8");

function sum($num){

     $tot = $num;

     echo "进入第{$num}层函数<hr style='border-style: dotted' />";

     if($num > 1){

             $tag = true;

            $sum = sum(--$num);  /*$sum = sum(--$num)之前是进入函数，之后是函数退出*/

             echo "<span style='color: red'>(\$tot => {$tot}) x (\$sum => {$sum}) <b>=</b> </span>";

            $tot *= $sum;

      }

      echo "<span style='color: red'>(\$tot => {$tot})</span><br />";

      if($tag){

             ++$num;

             echo "退出第{$num}层函数<hr />";

      }else{

             echo "退出第{$num}层函数<hr />";

      }

      return $tot;

}

echo "等于：" . sum(5);