title: How I can disable login page for users who logged in already
body: <p>How I can disable login page for users who logged in already? 
  I tried a lot to writing php code for "if user logged in already can't logged in again and can't see login page" but I didn't know </p>
  
  <pre><code>&lt;?php
      session_start(); 
  
      if(isset($_SESSION['user_name'])) 
      { 
          header('Location: home.php'); 
          exit;
      }
  ?&gt;
  </code></pre>