在C中为实数输入写一个简单的离散傅立叶变换

So I'm trying to write the Discrete Fourier Transform in C to work with real 32-bit float wav files. It reads in 2 frames at a time (one for each channel, but for my purposes I'm assuming they are both the same and so I use frame[0]). This code is supposed to write out the amplitude spectrum for an input file by probing it with frequencies 20,40,60,...,10000. I am using a Hanning window on the input frames. I want to avoid using complex numbers if I can. When I run this, it gives me some very strange amplitudes (most of which are extremely small, and are not associated with the correct frequencies), which makes me believe I am making a fundamental mistake in my computation. Can somebody offer some insight into what is happening here? Here is my code:So I'm trying to write the Discrete Fourier Tra