Add/Delete Items

[Dysan]

I have the following code, that displays a message whether a users shopping cart contains items or not.

How do I add/delete items from the shopping cart, upon the appropriate product link being clicked? If a items is already in the cart, how do I display a message notifying the user?

  $cart = $_SESSION['cart'];
  if (!$cart)
  {
    echo "You have no items in your shopping cart!";
  }
  else
  {
    echo "You have items in your shopping cart";
  }