Brush up on them!
From what I can remember, the trouble most people had in the Computer Architecture labs with C were pointers, arrays, memory allocation and casting (C will let you do whatever, but it might not work!)
Best way to brush up is to actually do some coding - grab gcc or some other C compiler (you can also set VC++ to only compile C code) and write a bunch of programs. Good places to start include Game of Life, Prime Numbers, String Encryption/Decryption
Another exercise we got students to do was to write a very simple processor simulator in C (and a basic assembler as well) - its not as hard as it sounds, and you can make it as complex as you want.
Enjoy!
