static void Main(string[] args) { //init singleton var terminal = new PointOfSaleTerminal(); //singleton cart //var terminal = PointOfSaleTerminal.Instance(); //add product code if Code not exit will print product not found, accept string or char terminal.ScanProduct("CCCCCCCCCCCC"); //cacualte the result decimal result = (decimal)terminal.CaculateTotal(); //write result to console Console.Write("${0:N2}", result); }