Hi, i have a problem of some days. I'm working to a website but when I installed it I have a very noticeable error page, I wrote: "Notice: Notice: Undefined index: user_name in C:\xampp\htdocs\index.php on line 118" How can I get rid of this writing. Thank you!

It is a message in Google Translate

The source of index.php:

<?PHP
// snipped irrelevant part

if(isset($_SESSION['user_admin']) && checkInt($_SESSION['user_admin']) && $_SESSION['user_admin']>=0) 
{
}

// snipped irrelevant part

<?php
if ( $_SESSION ["user_name"] == "") {
?>

Compare both remaining if's. If you use isset in the same way as the first, the notice will be gone.