I mean, I think at this point it is worth pointing out that you don’t need nested loops to solve this. What @admit8490 is saying is correct, but I think it’s building on a bad premise. If you want to solve it with the code you have, that’s fine. It’s probably a good idea just for understanding.
But you are using two, nested loops when all you really need is one loop. For the L2R diagonal, that is trivial. Borrowing from @admit8490 's good advice, list out the coordinates you need. Can you see how to get those with a single loop? What is the relationship between the two coordinates?
For the R2L do the same thing. Generating the second coordinate would be a tiny bit harder, not by much, and would involve a tiny bit of math. What is the relationship between the two coordinates?
Basically, my plan is to get just one line direction using one nested loop, which I got right. I was able to print the right diagonal from just one loop, but could not print the left diagonal with one loop. the L-diagonal should be (0,3)(1,2)(2,1)(1,3), but i couldn’t make it work