Dan,
Are you talking discrete or FFT?
There should be millions of code examples out there, but you have to be
careful about how they specify input & output (eg. Real vs. Imaginary, or
Modulus vs. Phase), especially for the FFT-based routines. (Make sure you
test on a known problem.)
I think I only have code in Fortran & QuickBasic, and I seem to remember
that the latter was a major pain to use (because of the input/output thing).
-- Al