Based on your original description I was expecting something more heavy on straight CS theory. “how do you sort an unordered binary tree in place“ kind of thing.
I was having a related conversation earlier, and feel like I'm reprising the same argument for a new audience, but... I don't see what is either Computer Science or theoretical about that. It seems like an eminently practical task: Handling things in a tree structure, sorting items, and doing work in-place to conserve resources are all very concrete, real-world aspects of writing software. You might not need them in _every_ case, but they aren't really "theory" in any real sense.
I turned down a job offer where the interviewer was more concerned about whether I could write a merge sort on the board (I did), than whether I could design a system. It told me a lot about the kind of people they hire.
I spent my first 12 years as a developer doing a lot of bit twiddling in C writing cross platform code with nothing but the standard library, but these days if someone asked me how to sort I would call a library function. Heck even C has a built in sort function.
You can argue that someone doesn't need something, that it's the wrong level of abstraction, or that it's not an appropriate interview question. I even agree to some degree. But that still doesn't make those "CS theory" subjects.
And some of the questions being posed (which are all expected to be solved in C) are a little tricky for me to figure out on my own without some of the niceties which I have been exposed to in higher level languages.
Perhaps the hardest of these was the Credit Card Validation example.
I was stuck for such a long time on trying to figure out how to utilise an array with for loops to multiply every second number of the card backwards.
This is Introduction to Computer Science and all of this is from week 1, so I was pretty much falling at the first hurdle.
The logic was there, but I still couldn't understand most of what was going on, unfortunately.
Through trial and error, I eventually managed to get something working.
>How can you write business logic at work without loops? It's not that I don't use them, it's that I have a hard time figuring out how to use them in the context of solving the problem.
I would forget about C, though, and try to do it in a language you already know to begin with.
To be honest I also find it very difficult to relate, as especially the Cesar Chiffre seems like such an easy problem. I only have to read it and my brain already maps out the solution. (I guess you could call it a No-Brainer, except that it seems to be a "Brainer" :-)
I honestly can not imagine how you usually code.
However, I want to say I remember my first year of studying mathematics. Many of the exercises also seemed very hard back then, but looking back on them the following year, they actually seemed quite easy (well, most of them). So practice and experience really can work. No guarantees, though.
Personally I like "Project Euler" for programming problems: https://projecteuler.net/ I actually had questions pop up in interviews that I had previously solved on project Euler.
Incidentally I describe my problems with math almost the exact same way - virtually nonexistent fundamental understanding, and so huge issues with abstracting out even the simplest real-world tasks. (My wake-up call was when I was basically just mashing buttons on my calculator one day when I realized I didn't know how to compute how much of X I could buy given that it was $Y per weight.)
Loops become super simple when you see them as series of steps with a yes/no question of whether to stop or go through your steps again.
Draw up some boxes for every variable you think you're going to need, give them labels and add the labels to the flowchart.
This then allows you to run through the flowchart step by step changing the values in each box as you go.
Maybe you're making it too complicated. The reason for loops is simply that you need to repeat an operation. Call it repetition if that helps.
- for x;y;z - repeat a specific number of times, or need an index #
- for x in y - iterate over container
- while x - repeat while a condition is true
- do while x - like while, but run at least once.
So, imagine we have a string and need to add 1 to each character. The second bullet above looks best, first if the language is lower level.
You probably lack in "coding"(maping solution to code) department - it's totally normal in language you don't work in day to day. You are probably less skilled in implementing simple, lower level abstractions - understandable given your background.
I have more exp than you - recently I was helping friend with python ML code - it took me 40 mins to code 20 lines. I don't feel bad at all, because even though I knew solution, to write it in python I had to google for each line and read docs to know range handling, dsl of libs, array comprehension syntax, lambdas etc.
Good news is that it's easy to get proficient fast by doing such exercises. I can recommend codewars.com