A good book that goes over both C and assembly is "Hacking: The Art of Exploitation". The first 100 pages alone will give you a solid understanding of what is happening behind the code.
I can't recommend that book for learning C and assembly. Its coverage is amateurish and unprofessional, which are indicative of or at least encourage fuzzy thinking. You can read it for a time-efficient overview, but please don't go thinking you know C or assembly if that's all you've read.
For clarification, the recommendation was not for learning C and assembly, but rather to get a good feel for what is happening at a lower level ie. stack frames, stack pointers, etc.
