public void add(Item item, int quantity)
 {
     totalPrice += item.price * quantity;
     totalQuantity += quantity;
     foreach(CartItem i in items)
     {
         if(i.item.ID == item.ID)
         {
             i.quantity += quantity;
             i.totalPrice += item.price * quantity;
             return;
         }
     }
     items.Add(new CartItem(item, quantity));
 }
 public CartItem(Item item, int quantity)
 {
     this.item = item;
     this.quantity = quantity;
     this.totalPrice = item.price * quantity;
 }
 public OrderLine(int ID, Item item, int quantity)
 {
     this.ID = ID;
     this.item = item;
     this.quantity = quantity;
 }