• Starting from the rightmost digit, form the sum of every other digit. For example, if the credit card number is 4358 9795, then you form the sum 5 + 7 + 8 + 3 = 23.
• Double each of the digits that were not included in the preceding step. Add all digits of the resulting numbers. For example, with the number given above, doubling the digits, starting with the next-to-last one, yields 18 18 10 8. Adding all digits in these values yields 1 + 8 + 1 + 8 + 1 + 0 + 8 = 27.
• Add the sums of the two preceding steps. If the last digit of the result is 0, the number is valid. In our case, 23 + 27 = 50, so the number is valid.
Write a program that implements this algorithm. The user should supply an 8-digit number, and you should print out whether the number is valid or not. If it is not valid, you should print the value of the check digit that would make it valid.
I have to use loops to do the sum. However, I do not know how to use loops for that.
Here's my code
card = input("Enter your credit card number here: ") digit_sum = 0 for i, digit in enumerate(reversed(card)): n = int(digit) if i % 2 == 0: digit_sum += n elif i >= 5: digit_sum += n * 2 - 9 else: digit_sum += n * 2 if digit_sum % 10 == 0: print("Card is valid!") else: print("Card is invalid!")