title: adding session variables to itself
body: <p>I need to add amounts if a customer buys more than one product. how to add using session variables. I stored the amount as  </p>
  
  <pre><code>$amount=$_POST['amount']
  $_SESSION['amount']=$amount;
  </code></pre>
  
  <p>doing the following thing isnt solving the problem  </p>
  
  <pre><code>$_SESSION['amount']+=$amount;
  </code></pre>