PHP: user is successfully logout but after logout refresh home page it shows that undefined variable:

Question

Email is the user session email after successfully logout there is no email exist but on index page is shows undefined index as there is no email after logout.

Notice: Undefined index: email in C:\xampp\htdocs\CMS\index.php on line 9
    <?session_start();
?>
<?php
    require("conection/connect.php");   
    $username=$_SESSION['email'];
    $sel= "select * from users where email= '$username'";
    $run_name = mysqli_query($con, $sel);
    $row_user=mysqli_fetch_array($run_name);
    $name=$row_user['name'];
    $userid=$row_user['user_id'];
    $teacherid=$row_user['teacher_id'];
    $userid=$row_user['stu_id'];
    $usertype=$row_user['type'];
?>

Answer 1

Just verify that it's set. That will probably be useful to you anyway, because I assume if it isn't set you may want to do something different.

<?php

if (!isset($_SESSION['email'])) {
    // maybe redirect to login?
    // or at least don't show them logged-in user type stuff
}

// your code (in an else block if you didn't redirect in the if)