Audio decoding CODEC_ID_MP3 cannot found

Does any one know what is the problem here?i cannot get mp3 codec~~~i'm using VS 2010 to develop~~thx for helping~~

Below is my code :
mp3codec = avcodec_find_decoder(CODEC_ID_MP3);

Post all your error messages.

There's no way we can tell what you did wrong from one line of code and "it doesn't work".