I want you to write kernel code for a few years. But we go to Lemmy with the machismo we have, not the machismo we wish we had. Write a JSON recognizer; it should have the following signature and correctly recognize ECMA 404, returning 0 on success and 1 on failure.
int recognizeJSON(const char*);
I estimate that this should take you about 120 lines of code. My prior estimated defect rate for C programs is about one per 60 lines. So, to get under par, your code should have fewer than two bugs.