Day 011: The Quiet Byte
K&R 1.8 and 1.9. Call by value, character arrays, and the single byte that holds all of C together.
Security
Day 010: The Memory Next Door
K&R 1.6 and 1.7. Arrays, character arithmetic, functions. And the first time I watched a bug disappear into memory that wasn't mine.
Day 007.5: The Exploit Lab
Day 004 What They Didn't Know
K&R section 1.4. Symbolic constants. The preprocessor. And the realization that every layer was built by people who could not see what was coming.