These problems remind me of the ones on checkio.org. The difference being over there you get the benefit of using python--not that I already knew python but it's rather intuitive, plus you can run a million things through an interpreter to quickly understand how it works. These CS50 problems require C, which most mortals would have a much harder time working with.
In either case you constantly consult the language reference and standard libraries until you find something that works. The C reference at https://reference.cs50.net/ looks perfectly good.
To be honest I don't know how I would load a CC# into an array to compute Luhn's algorithm on it in C. In Python I know there are easy ways of doing that, because strings are automatically arrays in the first place (same as that Caesar cypher problem, Python makes it much easier to work with strings). I don't even know if that's the "right" way to do it, but that's what I would do in Python: Convert the number to a string, operate on it as an array, converting each character to an int as it goes, running the algorithm as given in the problem, back-converting to string and then back again to int as needed (like if I need to add the digits of a number together). Fine I suppose I could avoid doing that by taking modulos and if I didn't know what a modulo was I would divide by 10 for instance and then take a floor to get the first digit of a 2-digit number.
I have no idea if any of these methods are "correct", I would just hammer away at the code until the acceptance tests passed. It would take over an hour for each of these solutions, after getting into the zone, so let's say 2 hours. There you go, 4 hours of work to get through these two problems in C, let's add on a lunch break and we have a full work day. That will be $325 thank you. Oh I don't get paid to study computer science in my free time? Oh ok. I guess I will just bookmark CS50 and come back to it... some day.
Your wife is lucky she gets to study this stuff. Don't be so hard on yourself.
In either case you constantly consult the language reference and standard libraries until you find something that works. The C reference at https://reference.cs50.net/ looks perfectly good.
To be honest I don't know how I would load a CC# into an array to compute Luhn's algorithm on it in C. In Python I know there are easy ways of doing that, because strings are automatically arrays in the first place (same as that Caesar cypher problem, Python makes it much easier to work with strings). I don't even know if that's the "right" way to do it, but that's what I would do in Python: Convert the number to a string, operate on it as an array, converting each character to an int as it goes, running the algorithm as given in the problem, back-converting to string and then back again to int as needed (like if I need to add the digits of a number together). Fine I suppose I could avoid doing that by taking modulos and if I didn't know what a modulo was I would divide by 10 for instance and then take a floor to get the first digit of a 2-digit number.
I have no idea if any of these methods are "correct", I would just hammer away at the code until the acceptance tests passed. It would take over an hour for each of these solutions, after getting into the zone, so let's say 2 hours. There you go, 4 hours of work to get through these two problems in C, let's add on a lunch break and we have a full work day. That will be $325 thank you. Oh I don't get paid to study computer science in my free time? Oh ok. I guess I will just bookmark CS50 and come back to it... some day.
Your wife is lucky she gets to study this stuff. Don't be so hard on yourself.