double cardTypeInterestAmount(string card) { creditCardType cardType = (creditCardType)Enum.Parse(typeof(creditCardType), card); switch (cardType) { case creditCardType.Visa: Visa visaCard = new Visa(); return visaCard.GetInterest(); case creditCardType.MasterCard: MasterCard mcCard = new MasterCard(); return mcCard.GetInterest(); case creditCardType.Discover: Discover discover = new Discover(); return discover.GetInterest(); } return 0.0; }