creditcard

Learning Objectives

• Algorithms
• I/O
• Data Representation

Abstract

In this project, you will create a tool called creditcard to:

• Validate credit card numbers.
• Generate possible card numbers.
• Get information about card brands and issuers.
• Issue new card numbers.

Context

Every computer program is a model, hatched in the mind, of a real or mental process.

— Alan J. Perlis. Structure & Interpretation of Computer Programs

Credit cards are used to pay for goods and services. Each card has a unique number that helps identify the cardholder and the issuing bank. Credit card numbers are long to ensure each card is unique. For example:

• Visa uses 13- and 16-digit numbers.
• MasterCard uses 16-digit numbers.
• American Express uses 15-digit numbers.

These numbers are not random. They follow specific patterns:

• Visa numbers start with 4.
• MasterCard numbers start with 51, 52, 53, 54, or 55.
• American Express numbers start with 34 or 37.

Credit card numbers also include a "checksum" that helps detect errors. This is done using Luhn's Algorithm, a simple math formula that checks if the number is valid.

Resources

• Anatomy of a Credit Card: The Luhn Algorithm Explained

General Criteria

• Your code MUST be written in accordance with gofumpt. If not, you will be graded 0 automatically.
• Your program MUST be able to compile successfully.
• Your program MUST not exit unexpectedly (any panics: nil-pointer dereference, index out of range etc.). If so, you will be get 0 during the defence.
• Only built-in packages are allowed. If not, you will get 0 grade.
• The project MUST be compiled by the following command in the project's root directory:

$ go build -o creditcard .

Mandatory Part

Validate

The validate feature checks if a credit card number is valid using Luhn's Algorithm.

Requirements:

• The number must be at least 13 digits long.
• If valid, print OK to stdout and exit with status 0.
• If invalid, print INCORRECT to stderr and exit with status 1.
• Support passing multiple entries.
• Support --stdin flag to pass number from stdin.

$ ./creditcard validate "4400430180300003"
OK
$ ./creditcard validate "4400430180300002"
INCORRECT
$ ./creditcard validate "4400430180300003" "4400430180300011"
OK
OK
$ echo "4400430180300003" | ./creditcard validate --stdin
OK
$ echo "4400430180300003" "4400430180300011" | ./creditcard validate --stdin
OK
OK

Generate

The generate feature creates possible credit card numbers by replacing asterisks (*) with digits.

Requirements:

• Replace up to 4 asterisks (*) with digits. If more - it's an error. Asterisks should be at the end of the given credit card number.
• Print the generated numbers to stdout.
• Numbers must be printed in ascending order.
• Exit with status 1 if there is any error.
• Support --pick flag to randomly pick a single entry.

$ ./creditcard generate "440043018030****"
4400430180300003
4400430180300011
4400430180300029
...
4400430180309988
4400430180309996
$ ./creditcard generate --pick "440043018030****"
4400430180304385

In case of an error:

$ ./creditcard generate --pick "44004301803*****"
$ echo $?
1

Information

The information feature provides details about the card based on data in brands.txt and issuers.txt.

Requirements:

• Output the card number, validity, brand, and issuer.
• Support --stdin flag to pass number from stdin.
• Support passing multiple entries.

$ ./creditcard information --brands=brands.txt --issuers=issuers.txt "4400430180300003"
4400430180300003
Correct: yes
Card Brand: VISA
Card Issuer: Kaspi Gold

In case of an incorrect card number:

4400450180300003
Correct: no
Card Brand: -
Card Issuer: -

Example content of brands.txt:

VISA:4
MASTERCARD:51
MASTERCARD:52
MASTERCARD:53
MASTERCARD:54
MASTERCARD:55
AMEX:34
AMEX:37

Example content of issuers.txt:

Kaspi Gold:440043
Forte Black:404243
Forte Blue:517792
Halyk Bonus:440563
Jusan Pay:539545

Notice, that both brands.txt and issuers.txt enumerate different kinds of a card, where each line consists of two parts. First part is the name of the kind and the second is the number prefix (i.e. numbers the card starts with). The parts are separated by : (two dots) symbol.

Issue

The issue feature generates a random valid credit card number for a specified brand and issuer.

Requirements:

• Pick a random number for the specified brand and issuer.
• Exit with status 1 if there is any error.

$ ./creditcard issue --brands=brands.txt --issuers=issuers.txt --brand=VISA --issuer="Kaspi Gold"
4400430180300003

Support

If you get stuck, try your code with the example inputs from the project. You should get the same results. If not, read the description again. Maybe you missed something, or your code is wrong. After the examples work, but your answer is still wrong, make some test cases you can check by hand. See if they work with your code. Use the complete example input.

If you are still stuck, ask a friend for help or take a break and come back later.

Guidelines from Author

Learn how to decompose problems

When you're trying to tackle a large project or problem, it's easy to become discouraged by just how big or intimidating the task seems. Instead of being intimidated, work on breaking the problem up (decomposing the problem) into smaller and smaller subproblems, until each individual subproblem seems manageable and doable.

Essentially, you're trying to gain the mindset of an engineer. If a problem is big, don't give up. Keep breaking it up into smaller and smaller pieces, and research things that seem irreducible. Then repeat, continuing the cycle: break down, google, break down, google...

This, by the way, is a pretty effective strategy for self-teaching!

Source: https://www.reddit.com/r/learnprogramming/wiki/faq/

Author

This project has been created by:

Alimukhamed Tlekbai, Team Lead at Doodocs.kz

Contacts:

• Email: [email protected]
• GitHub
• LinkedIn