I've been studying C off and on for about a month. I've got a pretty good grasp on things like functions, structs, and I'm working on file I/O and pointers again. My question is, when do you know enough to call yourself a programmer?

The book I'm using is "C Programming for the Absolute Beginner" and its chapters cover as follows.
1. C Fundementals
2. Beginning Data Types
3. Conditions
4. Looping Structures
5. Structured Programming
6. Arrays
7. Pointers
8. Strings
9. Advanced Structures and Data Types
10. Dynamic Memory Allocation
11. File Access
12. The C Preprocessor

While I know there is tons more to the C Language than what is covered in this book, I feel its a good start. So, after I get a good grasp on these beginning ideas, what should I focus on next? Whats going to make me the most useful as a programmer? Whats the next logical step in my education?

Thanks in advance for your help,
Michael