Here is a link of snippet in VB:

http://www.picbasic.co.uk/forum/show...=6731#post6731

And here is Roman Blacks DTMF decoder that is not using fourier but a rather smart approach to decode DTMF signals. It may be useful to you depending on the project.

https://www.romanblack.com/DTMF/DTMF_alg.htm

Ioannis