Data structures. I could understand control flow, looping, etc, but until I took the time to understand data structures, I was always copying example code and t

Data structures. I could understand control flow, looping, etc, but until I took the time to understand data structures, I was always copying example code and trying to guess at what would work. You can self teach yourself alot by learning as you go, but until I took the time to specifically study data structures I hadn't made it over the hump, my 'ah-ha' moment so to speak.