public static void returnAllChange()
        {
            Coin.returnChange(VendingMachine.totalAmountInserted);

            totalAmountInserted = 0;

            for (int i = 0; i < 4; i++)
            {
                allProduct[i].canPurchaseItem();
            }
        }
        public static void purchaseItem(Can product)
        {
            bool changeAvaliable = false;

            if (product.Stock > 0)
            {
                if (totalAmountInserted >= product.Price)
                {
                    changeAvaliable = Coin.returnChange(totalAmountInserted - product.Price);


                    if (changeAvaliable)
                    {
                        product.Stock--;

                        if (product.Stock <= 0)
                        {
                            product.flashSoldOut();
                        }

                        product.dispenseCan();

                        totalAmountInserted = 0;

                        for (int i = 0; i < 4; i++)
                        {
                            allProduct[i].canPurchaseItem();
                        }
                    }
                    else
                    {
                        noChangeLight.TurnOn3Sec();
                    }
                }
            }
        }