Why is my C code not finishing?

Question

A program which checks whether a credit card is legit or not by getting card no as input and fetching it to the algorithm .
It's a question from Harvard's CS50 intro to C class
Link to assignment: https://cs50.harvard.edu/x/2020/psets/1/credit/
https://code.sololearn.com/c30dG9MUz6G5/?ref=app

Answer 1

I didn't get it, what should I do

Answer 2

Thank you so much 🤗🤗