当我加载我的PHP页面然后提交按钮自动按和页面再次加载？

I'm using wamp server php my admin sql,table created connection every thing is fine,I'm working on local host, but page again and gain loading, not move down cursor etc, submit button automatically click ?

Here is screen shot http://i.imgur.com/QC6RtAg.jpg?1

       <center><form method="post">
       <table border="0" cellspacing="8">
       <tr>
          <td><label><b>*Select Campus:</b></label></td>
             <td>
            <select name="city" id="city">
                <option value="">-Please Select-</option>
                <option value="Isb">Islamabad</option>
                <option value="Abt">Abbotabad</option>
                <option value="wah">Wah</option>
                <option value="Atk">Attock</option>
                <option value="shw">Sahiwal</option>
                <option value="veh">Vehari</option>
                <option value="vir">Virtual</option>
            </select>
            <font color="red"><?php echo @$_GET['campus'];?></font>
       </td>
    </tr>
    <tr>
    <td><label><b>*Name</b></label></td>
    <td><input type="text" name="name" /> 
   <font color="red"><?php echo @$_GET['newname'];?></font>
   <td></tr>
   <br/>
    <tr>
   <td><label><b>*Login</b></label></td>
    <td><input type="text" name="logid"/>
    <font color="red"><?php echo @$_GET['logname'];?></font> 
    <td></tr>
    <br/>
    <tr>
   <td><label><b>*Email Address</b></label></td>
   <td><input type="text"type="require" name="email"/>
   <font color="red"><?php echo @$_GET['emailname'];?></font>
   </td></tr>
   <br/>
   <tr>
   <td><label><b>*Password</b></label></td>
   <td><input type="password" type="require" name="pass"/>
  <font color="red"><?php echo @$_GET['passname'];?></font>
  </td></tr>
 <br/>
 <tr>
<td><label><b>*Retype Password</b></label></td>
<td><input type="password" type="require" name="rpass"/>
<font color="red"><?php echo @$_GET['rpassname'];?></font>
</td></tr>

 </table>
 <table border="0">
 <tr id="bu">
 <td ><input type="submit" id="cl" value="sign up"name="submit"/></td>    </tr>

 </table>
 </form>
 </center>










 <?php
 $conn = mysqli_connect('localhost', 'root' , '','example');
 if(isset($_POST['submit']))<?php
 { 
$campus=$_POST['city'];
$name = $_POST['name'];
$u_id = $_POST['logid'];
$email = $_POST['email'];
$pass = $_POST['pass'];
$rpass = $_POST['rpass'];
if($campus==''){
echo
"<script>window.open('Log.php?campus=Select campus is    Required','_self')    
</script>";
exit();
}
if($name==''){
echo
"<script>window.open('Log.php?newname=Name is Required','_self')   </script>";
 exit();
 if($u_id==''){
echo
"<script>window.open('Log.php?logname=User ID is Required','_self')</script>";
        exit();
   }
   if($email==''){
   echo
  "<script>window.open('Log.php?emailname=Email is Required','_self')      </script>";
   exit();
  }
  if($pass==''){
   echo
   "<script>window.open('Log.php?passname=Password is Required','_self')   </script>";
    exit();
   }
   if($rpass==''){
   echo
   "<script>window.open('Log.php?rpassname=Password is Required','_self')  </script>";
exit();


}


 $sql = "INSERT INTO      student(Campus,User_id,Login,Email,password,Retype_password)    values('$campus','$name','$u_id','$email','$pass','$rpass')";

 if (mysqli_query($conn,$sql) {
echo "New record created successfully";
 print '<script>alert("Successfully Registered!");</script>'; // Prompts   the user
    print '<script>window.location.assign("login.php");</script>'; //   redirects to register.php
}     else {
 echo "Error: " . $sql . "<br>" . $conn->error;
 }$conn->close();
 }
?>