I am trying to make a library system, everything is going well, but I faced with such a error

> 
> Notice: Undefined index: user\_log in
>  C:\xampp\htdocs\e\_library\top.php on line 23
> 
> 
> 

and line 23 is here:

```
<?php 
$user_log = $_SESSION['user_log'];
if (isset($_SESSION['user_log'])){
    echo "<a href='#' style='color:#FFC'>Welcome $_SESSION[username] </a> ||  <a href='logout.php' style='color:#FFC'>Logout</a>";
}
else{
    echo "<a href='login.php' style='color:#FFC'>Sign In</a>";
}
?>

```