CS170: Programming for the World Around Us - Credit Card Validator (100 Points)
Assignment Goals
The goals of this assignment are:- To iterate over a list of data in Python
The Assignment
What to Do
Write a program to input a credit card number into a variable as a string of text. Loop over every character in the credit card number variable except for the very last one, and if the index is odd, double the value at that location (otherwise, just keep the number as-is). Add all the numbers together.
The ones digit of this sum should be equal to the last digit in the credit card number. Use the modulus operator to get the ones digit, and check if it equals the last digit in the credit card number. Print out whether or not they match.
Example
For example, suppose our credit card number is 5555555555554444. We can loop over each character in this string. If it is in an odd position (like the second 5, which is in index position 1), we can double it. Convert each digit to an int so you can double the values! From this, we get the following numbers:
Add these values together. For two digit values (like 16), we can convert the value back to a string, loop over its characters, convert them to int, and add them up. From these, we get the following values:
5
10
5
10
5
10
5
10
5
10
5
10
4
8
4
8
Adding these values together, we get 114. Take this number and mod it by 10, which obtains 4. This should match the last digit of the string, which it does! You can compare your calculated check digit and the last digit of the credit card string using an if statement. Just be sure to convert the last character of the credit card number to an int before you compare, so that you can compare it to your calculated integer value.
Helpful Functions
Looping over a string with its index
You can loop over each character of a string called str like this:
for i in range(len(str)):
ch = str[i]
# i is the position number of the character (the index)
# ch is the character itself
Converting a character to an integer
You can convert a character to an integer using the int function:
x = int(x)
Extra Credit (10%): Adding the Individual Digits
Some credit cards add the individual digits together. So, after multiplying by 2, if you get 12, you add 1 + 2 instead of 12. To do this, convert the value back to a string using:
ch = str(ch)
And loop over those characters (like before), adding them to the sum instead.
Extra Credit (10%): argv
Modify your program to get the credit card number from sys.argv. sys.argv is an array of command line arguments. sys.argv[0] is the name of the program itself, and subsequent arguments are those you type in at the console when you run the program. Normally, when you click the run button, the shell runs:
python yourprogram.py
But you can do this manually by typing
python creditcard.py 1234567890123456
which will place 1234567890123456 into sys.argv[1]. Be sure to import the sys library and if the length of this array is at least 2, use sys.argv[1]. Otherwise, use the input function to get the credit card number like before. Run the program from the command line. This is a convenient way to bypass having to pause your program to wait for user input!
What to Turn In
When you’re done, write a README for your project, and save all your files, before exporting your project to ZIP. In your README, answer any bolded questions presented on this page. In addition, write a few paragraphs describing what you did, how you did it, and how to use your program. If your program requires the user to type something in, describe that here. If you wrote functions to help solve your problem, what are they, and what do they do? Imagine that you are giving your program to another student in the class, and you want to explain to them how to use it. What would you tell them? Imagine also that another student had given you the functions that you wrote for your program: what would you have wished that you knew about how to call those functions?
Submission
In your submission, please include answers to any questions asked on the assignment page in your README file. If you wrote code as part of this assignment, please describe your design, approach, and implementation in your README file as well. Finally, include answers to the following questions:- Describe what you did, how you did it, what challenges you encountered, and how you solved them.
- Please answer any questions found throughout the narrative of this assignment.
- If collaboration with a buddy was permitted, did you work with a buddy on this assignment? If so, who? If not, do you certify that this submission represents your own original work?
- Please identify any and all portions of your submission that were not originally written by you (for example, code originally written by your buddy, or anything taken or adapted from a non-classroom resource). It is always OK to use your textbook and instructor notes; however, you are certifying that any portions not designated as coming from an outside person or source are your own original work.
- Approximately how many hours it took you to finish this assignment (I will not judge you for this at all...I am simply using it to gauge if the assignments are too easy or hard)?
- Your overall impression of the assignment. Did you love it, hate it, or were you neutral? One word answers are fine, but if you have any suggestions for the future let me know.
- Using the grading specifications on this page, discuss briefly the grade you would give yourself and why. Discuss each item in the grading specification.
- Any other concerns that you have. For instance, if you have a bug that you were unable to solve but you made progress, write that here. The more you articulate the problem the more partial credit you will receive (it is fine to leave this blank).
Assignment Rubric
| Description | Pre-Emerging (< 50%) | Beginning (50%) | Progressing (85%) | Proficient (100%) |
|---|---|---|---|---|
| Algorithm Implementation (60%) | The algorithm fails on the test inputs due to major issues, or the program fails to compile and/or run | The algorithm fails on the test inputs due to one or more minor issues | The algorithm is implemented to solve the problem correctly according to given test inputs, but would fail if executed in a general case due to a minor issue or omission in the algorithm design or implementation | A reasonable algorithm is implemented to solve the problem which correctly solves the problem according to the given test inputs, and would be reasonably expected to solve the problem in the general case |
| Code Quality and Documentation (30%) | Code commenting and structure are absent, or code structure departs significantly from best practice, and/or the code departs significantly from the style guide | Code commenting and structure is limited in ways that reduce the readability of the program, and/or there are minor departures from the style guide | Code documentation is present that re-states the explicit code definitions, and/or code is written that mostly adheres to the style guide | Code is documented at non-trivial points in a manner that enhances the readability of the program, and code is written according to the style guide |
| Writeup and Submission (10%) | An incomplete submission is provided, or the README file submitted is blank | The program is submitted, but not according to the directions in one or more ways (for example, because it is lacking a readme writeup or missing answers to written questions) | The program is submitted according to the directions with a minor omission or correction needed, including a readme writeup describing the solution and answering nearly all questions posed in the instructions | The program is submitted according to the directions, including a readme writeup describing the solution and answering all questions posed in the instructions |
Please refer to the Style Guide for code quality examples and guidelines.