求大神帮忙看看哪里错了

if (!isset($_SESSION["sn"])){$_SESSION['sn']=0;setcookie('sn',$sn,time()+1);    if($_POST["submit"]){	if($sn=3)	{

alert("抱歉，您已经点击了3次");			location.href="zp.php";

exit();	}	elseif ($sn=="tull")	{

alert("123");			location.href="zp.php";

exit();	}	$newitem=$_POST["zp_user"];		$sql="insert into vote (awards,sn,pnone) values (1,'$sn',1)";	if(mysql_query($sql))	{    		$sn==$_SESSION['sn']+1;	}}	if($_POST["submit2"]){		if(empty($_POST['sn']))$_SESSION['zp_user']=$_POST['pnone'];$sql="insert into zp_user values('".($_POST['sn'])."')";	if(mysql_query($sql))	{		}}}

回复讨论(解决方案)

if(mysql_query($sql))
    {    
        $sn ==$_SESSION['sn']+1;
     
}
为何用==？

代码怎么都是分开的，这样很难看得到……

    if($_POST["submit"]){
    if($sn =3)
应为 ==

if($_POST["submit"]){
    if($sn=3)  // ==
    {

= 是赋值
== if条件判断才用到