Here a simple exercise I had to do for Computer Graphics class.

An implementation of an analog clock synchronised with local system time. (I used the tm structure, so is working only on *nix like operating system).

I resync my clock each minute using Synchronise(). (not very needed cause
glutTimer is quite reliable)

To compile:
$ gcc -o clock -lGL -lglut clock.c

Download source (clock.c)