A Quine is a computer program which produces its own source code as the (only) output.
With the help of printf(), we can make a quine in 117 bytes of error- and warning-free C code (tested GCC 4.2).
However, with a little trickery, we can reduce it down to just 74 bytes. The compiler will complain, but we really don't need the #include (GCC links against the C library automatically). We can also save 2 bytes by replacing char with int. Who needs types, right? Bytes are bytes.
$ ./a.out > tmp
$ diff tmp quine.c