Credit

Implement a program that determines whether a provided credit card number is valid according to Luhn’s algorithm.

$ python credit.py
Number: 378282246310005
AMEX

Accepting this Assignment

  1. Accept this assignment via GitHub Classroom.
  2. After about a minute, refresh the page and ensure you see “You’re ready to go!”.

Getting Started

Log into code.cs50.io, click on your terminal window, and execute cd by itself. You should find that your terminal window’s prompt resembles the below:

$

Next execute

get50 sentimental-credit

in order to download a directory called sentimental-credit into your codespace.

Then execute

cd sentimental-credit

in order to change into that directory. Your prompt should now resemble the below:

sentimental-credit/ $

Execute ls by itself, and you should see a few files and folders:

credit.py

If you run into any trouble, follow these same steps again and see if you can determine where you went wrong!

Specification

  • In credit.py, write a program that prompts the user for a credit card number and then reports (via print) whether it is a valid American Express, MasterCard, or Visa card number, exactly as you did in Problem Set 1, except that your program this time should be written in Python.
  • So that we can automate some tests of your code, we ask that your program’s last line of output be AMEX\n or MASTERCARD\n or VISA\n or INVALID\n, nothing more, nothing less.
  • For simplicity, you may assume that the user’s input will be entirely numeric (i.e., devoid of hyphens, as might be printed on an actual card).
  • Best to use get_int or get_string from CS50’s library to get users’ input, depending on how you to decide to implement this one.

Usage

Your program should behave per the example below.

$ python credit.py
Number: 378282246310005
AMEX

Hints

  • It’s possible to use regular expressions to validate user input. You might use Python’s re module, for example, to check whether the user’s input is indeed a sequence of digits of the correct length.

Testing

While check50 is available for this problem, you’re encouraged to first test your code on your own for each of the following.

  • Run your program as python credit.py, and wait for a prompt for input. Type in 378282246310005 and press enter. Your program should output AMEX.
  • Run your program as python credit.py, and wait for a prompt for input. Type in 371449635398431 and press enter. Your program should output AMEX.
  • Run your program as python credit.py, and wait for a prompt for input. Type in 5555555555554444 and press enter. Your program should output MASTERCARD.
  • Run your program as python credit.py, and wait for a prompt for input. Type in 5105105105105100 and press enter. Your program should output MASTERCARD.
  • Run your program as python credit.py, and wait for a prompt for input. Type in 4111111111111111 and press enter. Your program should output VISA.
  • Run your program as python credit.py, and wait for a prompt for input. Type in 4012888888881881 and press enter. Your program should output VISA.
  • Run your program as python credit.py, and wait for a prompt for input. Type in 1234567890 and press enter. Your program should output INVALID.

Execute the below to evaluate the correctness of your code using check50. But be sure to compile and test it yourself as well!

check50 cs50/problems/2021/fall/sentimental/credit

Execute the below to evaluate the style of your code using style50.

style50 credit.py

This problem will be graded only along the axes of correctness and style.

How to Submit

In your terminal window, execute the below.

submit50 sentimental-credit

You may submit as many times as you would like up until the deadline. To confirm your submission, go to https://github.com/classroom50/sentimental-credit-USERNAME, where USERNAME is your GitHub username. You should see the code from your latest submission.