求大神帮忙看看错哪了

求大神帮忙看看哪里错了

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

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

exit();<br />	}<br />	elseif ($sn=="tull")<br />	{

alert("123");<br />			location.href="zp.php";

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

------解决方案--------------------
if(mysql_query($sql))
    {    
        $sn==$_SESSION['sn']+1;
     
}
为何用==？
------解决方案--------------------
代码怎么都是分开的，这样很难看得到……
------解决方案--------------------
    if($_POST["submit"]){
    if($sn=3)
应为 ==

------解决方案--------------------
if($_POST["submit"]){
    if($sn=3)  // ==
    {

------解决方案--------------------
= 是赋值
== if条件判断才用到