Personally, the hardest part for me was keeping track of the size of everything. Coming from a higher level language, keeping track of the bits and bytes takes some getting used to. Working with arrays in C is much tougher especially when the compiler will compile almost anything you give it, and even a small mistake is catastrophic.

Before C, I was pampered and took everything for granted. Now I appreciated my life more after C and feel blessed every time my IDE gives me a warning.