Web比赛4

<?php 
#这不是抽奖程序的源代码！不许看！ 
header("Content-Type: text/html;charset=utf-8"); 
session_start(); 
if(!isset($_SESSION[‘seed‘])){ 
$_SESSION[‘seed‘]=rand(0,999999999); 
} 

mt_srand($_SESSION[‘seed‘]); 
$str_long1 = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
$str=‘‘; 
$len1=20; 
for ( $i = 0; $i < $len1; $i++ ){ 
    $str.=substr($str_long1, mt_rand(0, strlen($str_long1) - 1), 1);        
} 
$str_show = substr($str, 0, 10); 
echo "<p id=‘p1‘>".$str_show."</p>"; 


if(isset($_POST[‘num‘])){ 
    if($_POST[‘num‘]===$str){x 
        echo "<p id=flag>抽奖，就是那么枯燥且无味，给你flag{xxxxxxxxx}</p>"; 
    } 
    else{ 
        echo "<p id=flag>没抽中哦，再试试吧</p>"; 
    } 
} 
show_source("check.php");