title: Updating the quantity if item already exists in cart
body: <p>Hi all so I managed to get the subtotal of all items in my cart thankyou to stack overflow user KyleK. The last functionality that im having problems with is adding 1 to the quantity of  a particular item in the cart if that item already exits. At the minute if I click add to basket twice then the same item is listed twice. Instead it would be great to have the item listed once with the quantity of two if this makes sense.</p>
  
  <p>Thankyou in advance.</p>
  
  <p>My code is located here at stack overflow.</p>
  
  <p><a href="https://stackoverflow.com/questions/17129590/i-need-help-getting-the-grand-total-of-a-simple-php-cart-using-sessions">My Code</a></p>