Problem Set 6: Cash and credit

#CASH

while True:
    cash_input = input("Enter amount: ")
    try:
        cash = float(cash_input)
        if cash > 0:
            break
        else:
            print("Invalid input. Please enter a positive number.")
    except ValueError:
        print("Invalid input. Please enter a valid number.")

coins = round(cash * 100)

count = 0
while coins > 0:
    if coins >= 25:
        coins -= 25
        count += 1
    elif coins >= 10:
        coins -= 10
        count += 1
    elif coins >= 5:
        coins -= 5
        count += 1
    else:
        coins -= 1
        count += 1

print(count)


#CREDIT

def luhn_algorithm(card_number):
    digits = list(card_number[::-1])
    total_sum = 0

    for i in range(len(digits)):
        digit = int(digits[i])

        if i % 2 == 1:
            digit *= 2

            if digit > 9:
                digit -= 9

        total_sum += digit

    if total_sum % 10 == 0:
        return True
    else:
        return False

card_number = input("Enter card number: ")
card_number = card_number.strip()

length = len(card_number)
if length < 13 or length > 16:
    print("INVALID")
else:
    if luhn_algorithm(card_number):
        if card_number[:1] == '4':
            print("VISA")
        elif card_number[:2] in ["34", "37"]:
            print("AMEX")
        elif card_number[:2] >= '51' and card_number[:2] <= '55':
            print("MASTERCARD")
    else:
        print("INVALID")