# functions go here
def cash_credit(question):

    while True:
        response = input(question).lower()

        if response == "cash" or response == "ca":
            return "cash"

        elif response == "credit" or response == 'cr':
            return "credit"

        else:
            print("Please choose a valid payment method")

# Main routines goes here
while True:
    payment_method = cash_credit("Choose a payment method (cash" " or credit): ")


    print("You choose", payment_method)

    print("program continues...")
    print()