Notice: Undefined index: stuname in Z:\Apache24\htdocs\7.php on line 14


<?php
$conn=mysqli_connect('localhost', 'root', 'mysql2016', 'course');
mysqli_query($conn,'set names utf8');
session_start();
//$name=$_GET['name'];
//$typename=$_GET['typename'];
//$score=$_GET['score'];
 $name = isset($_GET['name'])? $_GET['name'] : 0;
 $typename = isset($_GET['typename'])? $_GET['typename'] : 0;
 $score = isset($_GET['score'])? $_GET['score'] : 0;  
 $sno = isset($_GET['sno'])? $_GET['sno'] : 0;
 $stuname=$_SESSION['stuname'];
 $sqlstr="SELECT name FROM kecheng WHERE  name ='$name'  ";
$result=mysqli_query($conn,$sqlstr) or die();
$row=mysqli_fetch_array($result); 
if($row)
{
echo"<script>alert('您你已经选了此课程！');history.go(-1)</script>";
 }
else
 {
    if(mysqli_query($conn,"insert into kecheng(name,typename,score,sno,stuname)values('$name','$typename','$score','$sno','$stuname')"))
{
   echo"<script>alert('操作成功！');location.href='6.php'</script>";
}
else
{
echo"<script>alert('操作失败！');history.go(-1)</script>";
}
 }
?>
新手一枚，求帮助，为什么执行不了