title: Code Igniter PHP Error - Message: Use of undefined constant
body: <p>Im loading different contents in my main view with my menu, the code is working properly but is i have this error message.</p>
  
  <pre><code>A PHP Error was encountered
  Severity: Notice
  Message: Use of undefined constant users - assumed 'users'
  Filename: views/welcome.php
  Line Number: 53
  A PHP Error was encountered
  Severity: Notice
  Message: Use of undefined constant stores - assumed 'stores'
  Filename: views/welcome.php
  Line Number: 56
  A PHP Error was encountered
  Severity: Notice
  Message: Use of undefined constant notes - assumed 'notes'
  Filename: views/welcome.php
  Line Number: 59
  </code></pre>
  
  <p>This is my view</p>
  
  <pre><code>            &lt;div id="nav"&gt;
              &lt;div id="imagesBox"&gt;
                  &lt;a href="index.php?section=users"&gt;&lt;img class="imagesLeft" src="images/usuario_on.png"&gt;&lt;/a&gt;
                  &lt;a href="index.php?section=stores"&gt;&lt;img class="imagesLeft" src="images/tienda_on.png"&gt;&lt;/a&gt;
                  &lt;a href="index.php?section=notes"&gt;&lt;img class="imagesLeft" src="images/aviso_on.png"&gt;&lt;/a&gt;
          &lt;/div&gt;
          &lt;?php
          $section; $users=0;
          switch ($_GET['section']) {
          case users:
              $this-&gt;load-&gt;view('users'); 
              break;
          case stores:
              $this-&gt;load-&gt;view('stores'); 
              break;
          case notes:
              $this-&gt;load-&gt;view('notes'); 
              break;
      }
  
  ?&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>And this is my controller (im using tank_auth and is working properly)</p>
  
  <pre><code>class Welcome extends CI_Controller
  {
      function __construct()
      {
          parent::__construct();
  
          $this-&gt;load-&gt;helper('url');
          $this-&gt;load-&gt;library('tank_auth');
      }
      function index()
      {
          if (!$this-&gt;tank_auth-&gt;is_logged_in()) {
              redirect('/auth/login/');
          } else {
              $data['user_id']    = $this-&gt;tank_auth-&gt;get_user_id();
              $data['username']   = $this-&gt;tank_auth-&gt;get_username();
              $this-&gt;load-&gt;view('welcome', $data);
          }
      }
  }
  </code></pre>
  
  <p>I dont find the best method to fix this and this is a little weird, because the code is working like i want.</p>