Goto, scoping rules, function prototypes. 

Fun stuff. Also includes test cases for those things.

I hope you're not put off by the use of 2-token lookahead for parsing statement labels. If it's any consolation, GCC does a similar thing as seen on line 4533 of http://gcc.gnu.org/git/?p=gcc.git;a=blob_plain;f=gcc/c/c-parser.c;hb=refs/heads/trunk