making functions take arrays

Is it possible to make a compiled C function take an array as an
argument?  Right now I've got a function that takes 32 arguments, all
declared as separate variables (int arg1, int arg2, ...) and it would
be a lot more natural for the function to be called with an array (int
*array, int num_elements).  Is this possible?

Also, how do I return an SQL NULL from a function?

Thanks,
Kyle