how to convert pcm16 to pcm8?

WAVEFORMATEX in_wfx;
in_wfx.wFormatTag = WAVE_FORMAT_PCM;
in_wfx.nChannels =1;
in_wfx.nSamplesPerSec =8000;
in_wfx.nAvgBytesPerSec =16000;
in_wfx.nBlockAlign =2;
in_wfx.wBitsPerSample =16;
in_wfx.cbSize = 0;

WAVEFORMATEX out_wfx;
out_wfx.wFormatTag = WAVE_FORMAT_PCM;
out_wfx.nChannels =1;
out_wfx.nSamplesPerSec =8000;
out_wfx.nAvgBytesPerSec =8000;
out_wfx.nBlockAlign =1;
out_wfx.wBitsPerSample =8;
out_wfx.cbSize = 0;