//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;
}