An excellent How To book on the C language is the "C Primer Plus" by the Waite
Group, published by Sams. You probably should also pick up a copy of "The C
Programming Language" by Kernighan and Ritchie (the famous K&R). Though it this
is less a textbook than a language definition, it does include exercises.
Opinion on the preferred compiler seems to be split. Those who want to link C
segments with Amiga Assembler modules are opting for Lattice. The C-only folks
are heavily in favor of Aztec C, for its fast compile/execute times and smaller
code size. You pays your money and you takes your chance.