c_dec =01 + (02/60);
The return value in the function definition is "deg"; you calculate "c_dec" instead.
your choice will fix the problem. (I'd probably choose the latter, but it's your call).
I think "O1, O2" are remarkably uninformative choices for dummy argument variable names, however; I'd strongly recommend something that has some indication of what they are. The 'puter doesn't care; but would make maintenance in future easier as well as give somebody else at least a chance to know what is what. There are no comments in sight, either...