The C and Java helpdesk are now located at the Duty Programmers' Office (10.10.13). You must book a session on the staff booking page first. C and Java help is only available when there are multiple DPs on duty.
The best place to ask general C-related questions is on the rmit.cs.lang.c newsgroup. This group is read by most C helpers, many lecturers and other staff at RMITCS
To subscribe to the group in tin or rtin, hit shift-s at the initial group menu and enter "rmit.cs.lang.c".
If you need information on a specific C function you can look it up in section 3 of the man pages on Yallara or Numbat. For example, to get information on the printf() function, enter:
man -s 3 printf
The Stanford CS Library has many useful materials, including: