status.i4.v = wn_data_fft_c(return_type.i4.v, out_real.r4p.r,
				    out_imaginary.r4p.r, num_fft.i4.r

	This routine computes the Fast Fourier Transformation (FFT) for the
	the saved data set for the active graphic window.  The calling
	program is responsible for freeing the out_real, out_imaginary, and
	out_amp buffers.  (Note: The returned data arrays have the zero
	frequency component in the first entry.  This is followed by the
	smallest nonzero positive frequency component.  Positive frequencies
	increasing in magnitude are stored in the following locations up
	to entry num_fft/2.  After this are stored the negative frequencies
	with the most negative frequency component in the last entry.)

	return_type	returned data type requested
			(WN_FFT -> return discrete Fourier transform,
			 WN_FFT_NORMALIZED -> return normalized discrete
					      Fourier transform,
			 WN_INVERSE_FFT -> return (exponent power of 2)
					   times the inverse discrete
					   Fourier transform)
	out_real	returned array of real FFT coefficients
	out_imaginary	returned array of imaginary FFT coefficients
	num_fft		returned length of FFT arrays
	out_amp		returned array of FFT amplitude values

	This function returns ACNET status values as follows:

	OK			success
	CBS_INVARG		invalid isign value
	CBS_NOSETUP		an active window has not been established
				or no data is saved
	CBS_MEMFAIL		failed in allocating dynamic memory
	CBS_NODAT		no valid data points for this request

	This function requires the following include files:

	cbslib_h, acnet_errors_h

	Related functions:

	wn_data_save(_c), wn_data_set_cut_c, wn_data_mean, wn_data_extrema,
	wn_data_recall, wn_data_query, wn_data_polyfit_c, intro_graphics_windows

	C/C++ usage:

	int	status;
	int	return_type = WN_FFT;
	int	num_fft;
	float	*out_real;
	float	*out_imaginary;
	float	*out_amp;

	status = wn_data_fft_c(return_type,&out_real,&out_imaginary,