<?php

 class RandString{

     //这个属性表示我们随机数的长度，也就是个数

     private $length;

     //要哪些类型type为1的时候就是数字类型的，为2的时候字母类型，为3的时候就是数字加上字母的随机数

     private $type;

     public function __construct($length,$type){

         $this->length=$length;

         $this->type=$type;

     }

     public function randNum(){

         switch ($this->type){

             case 1:

                 return join(array_rand(range(0, 9),$this->length));

                 break;

             case 2:

                 return join(array_rand(array_flip(array_merge(range('a', 'z'),range('A', 'Z'))),$this->length));

                 break;

             case 3:

                 return join(array_rand(array_flip(array_merge(range(0, 9),range('a', 'z'),range('A', 'Z'))),$this->length));

                 break;

         }

     }

 }

 $strNum = new RandString(4,1);

 echo $strNum->randNum();

 echo '<hr/>';

 $strNum = new RandString(4,2);

 echo $strNum->randNum();

 echo '<hr/>';

 $strNum = new RandString(4,3);

 echo $strNum->randNum();

 echo '<hr/>';

 echo '<hr/>';

 echo '<hr/>';

 echo print_r(range('a', 'z'));

 echo '<hr/>';

 echo print_r(array_flip(range('a', 'z')));

 echo '<hr/>';

 echo print_r(array_merge(range(0, 9),range('a', 'z'),range('A', 'Z')));

 echo '<hr/>';

 echo print_r(array_flip(array_merge(range(0, 9),range('a', 'z'),range('A', 'Z'))));

 echo '<hr/>';