//Method to be called in case of new transaction
        public void newTransaction()
        {
            ProductDataSource pds = new ProductDataSource();

            //++number;
            foreach (WCSA_Entity_Classes.Product prd in purchaseList)
            {
                pds.ModifyItemInAccordanceWithInvoice(prd.ProductCode, prd.Quantity);
            }

            purchaseList.Clear();
            totalCost = 0;
        }