public CashContext(string type)
        {
            switch (type)
            {
            case "正常收費":
                cs = new CashNormal();
                break;

            case "滿三百送一百":
                CashReturn cs1 = new CashReturn("300", "100");
                cs = cs1;
                break;

            case "打八折":
                CashRebate cs2 = new CashRebate("0.8");
                cs = cs2;
                break;
            }
        }
        public static CashSuper createCashAccept(string type)
        {
            CashSuper cs = null;

            switch (type)
            {
            case "正常收費":
                cs = new CashNormal();
                break;

            case "滿三百送一百":
                CashReturn cs1 = new CashReturn("300", "100");
                cs = cs1;
                break;

            case "打八折":
                CashRebate cs2 = new CashRebate("0.8");
                cs = cs2;
                break;
            }
            return(cs);
        }