title: Session variables lost between pages
body: <p>In a page, two variables are passed in a URL.</p>
  
  <p>In the second page, these variables are initialized. At submit, new page open. The problem is here, I can't recover the session variables. </p>
  
  <p>The script indicate a error (undefined index).</p>
  
  <p>Thanks for help in advance.</p>
  
  <p>Here the code :</p>
  
  <p><strong>First page</strong> : </p>
  
  <pre><code>&lt;?php
  $requete_cours="SELECT COURS.SIGLE AS SIGLE, ANNEE FROM COURS, MODULE WHERE           COURS.ID_MODULE = MODULE.ID_MODULE and ID_PERSONNE = $userid";
  //$requete_cours;   
  $res = mysqli_query($cxn, $requete_cours);
  echo (mysqli_error ($cxn));
  while($ligne = mysqli_fetch_array($res)){
  echo '&lt;a href="professeur_absences.php?classe='.$ligne['ANNEE'].'&amp;amp;cours='.$ligne['SIGLE'].'"&gt;';
  echo $ligne['ANNEE'].' - '.$ligne['SIGLE'].'&lt;/a&gt;';
  echo '&lt;br/&gt;';
  }   
  ?&gt;  
  </code></pre>
  
  <p><strong>Second page</strong> :</p>
  
  <pre><code>$_SESSION['classe'] = $_GET['classe'];
  $_SESSION['cours'] = $_GET['cours'];
  </code></pre>
  
  <p><strong>Third page</strong> :</p>
  
  <pre><code>if(isset($_REQUEST['afficher'])){
      $semaine = $_REQUEST['semaine'];
      $classe = $_SESSION['classe'];
      $cours = $_SESSION['cours'];
      $_SESSION['semaine'] = $semaine;
      $requete_cours_id = "SELECT ID_COURS FROM COURS WHERE SIGLE = $cours";
      //echo $requete_cours;  
      $res = mysqli_query($cxn, $requete_cours_id);
      echo (mysqli_error ($cxn));
      $coursId = mysqli_fetch_array($res);
  </code></pre>