memory layout of 32 bit and 64 bit.Data segements . Where is memory allocated to any thing.Pointers and specially bitwise operators. Recursion etc is a must. You must be really proficient in C to clear this interview. Knowledge of memory is required that were would be a certain memory allocated when do perform a task. Dynamic memory allocation etc.It is not easy as it seems to be,one should learn let us c book by heart.