包括傅里叶变换和傅里叶反变换，c语言编写，简单明了，VC环境验证通过,Including Fourier transform and Fourier inverse transform, c language, simple and clear, VC verification environment through the

双音多频（DTMF）拨号中，通过计算FFT来判定按键所产生的频率。-DTMF dialing, through the FFT calculation to determine the frequency of generated keys.

cython写的DTMF解码器（python直接使用，效率和c接近）-cython write DTMF decoder (python direct use, efficiency, and c close)