What compiler are you using...
If it's not going past 16 bits I'm guessing you're using some old DOS version of Turbo C... which has been obsolete for more than a decade.
Grab a newer compiler... Pelles C is a good choice. When you download it spend some time in the help file and learn what's going on before you do any coding... In particular look up the tutorial on making your first project.
... or use a long type.
FYI: It is normally not allowed to use a loop in a recursive function by the teachers doing the grading.
Tim S.
"...a computer is a stupid machine with the ability to do incredibly smart things, while computer programmers are smart people with the ability to do incredibly stupid things. They are,in short, a perfect match.." Bill Bryson
@OP: Also learn about bitwise shifts (<< and >>), because they'll help you in this situation.
