### Luhn's Test of Credit Card Numbers (Due 23 Sep 2013)

In this program you will test whether a given 16-digit credit card number is valid or not. Here are the steps in your program:

• You will prompt the user to enter a 16-digit credit card number.
• You will read the credit card number in as an int.
• You will perform the Luhn's test (outlined below).
• You will then print if the credit card number is valid or not.
You will be making the following assumptions:
• The user enters only digits.
• The user enters exactly 16 digits.
Here are possible scenarios that may happen. Your output statements must be exactly the ones specified. Points will be deducted for variations.

#### Scenario 1

```Enter 16-digit credit card number: 1234567891234567

Invalid credit card number
```

#### Scenario 2

```Enter 16-digit credit card number: 4222222222222220

Valid credit card number
```

Luhn's Test: Let us say that the credit card number was made of the following digits:

d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12 d13 d14 d15 d16

Then the Luhn's algorithm goes as follows:

• Multiply all the odd digits d1, d3, … d15 by 2.
• Sum the digits of each product.
• Now add all the even digits d2, … d16 and the single digit products of the odd digits.
• If the final sum is divisible by 10 then the credit card is valid, otherwise it is invalid.

Here are two examples worked out - one is a valid credit card number and the other is an invalid credit card number.

 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12 d13 d14 d15 d16 4 4 3 2 3 3 3 8 8 4 1 3 8 3 4 3 8 6 6 6 16 2 16 8 8 6 6 6 7 2 7 8 8 4 6 2 6 3 6 8 7 4 2 3 7 3 8 3

The sum of the digits is 80. It is divisible by 10 and hence the credit card number is valid.

 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12 d13 d14 d15 d16 8 2 7 3 1 2 3 2 7 3 5 1 0 5 6 9 16 14 2 6 14 10 0 12 7 5 2 6 5 1 0 3 7 2 5 3 2 2 6 2 5 3 1 1 0 5 3 9

The sum of the digits is 56. It is not divisible by 10 and hence the credit card number is invalid.

You must first write the pseudo code version of this algorithm. You do NOT have to submit the pseudo code. Once you have the pseudo code then you can translate that to Python.

To obtain the last digit of a number use the modulo (%) operator. To remove the last digit of a number divide by 10. Here are snippets of code that will help you with your Python program.

```  # Prompt the user to enter the credit card number
credit_card = int (input ('Enter 16-digit credit card number: '))

# Get digit d16
d16 = credit_card % 10

# Get digit d15
cc = credit_card // 10
d15 = cc % 10

# Multiply odd digit by 2 and sum digits
d15 = d15 * 2
sum_d15 = (d15 % 10) + (d15 // 10)

# Final validity test for the sum of digits
if (sum_digits % 10 == 0):
print (...)
else:
print (...)
```

The program that you will be writing will be called CreditCard.py. We will be looking at good documentation, and adherence to the coding convention mentioned in class.

• Your variable names will be in lower case.
• You will use meaningful variable names where ever possible.
• You will indent by two spaces.
• All your code must be within def main():
• There must be a final call to main().

```#  File: CreditCard.py

#  Description:

#  Student Name:

#  Student UT EID:

#  Course Name: CS 303E

#  Unique Number:

#  Date Created: