Implementing a neural network is not very easy task. For some, it may be even impossible. This site offers C implementation of various types of neural networks including ADALINE, Multi-layer Feedforward NN (they call it Back-Propagation Network which is not correct. BP is a learning method and not an architecture), Hopfield, Self Organization Network (SOM), Adaptive Resonance Theory 1 (ART1), and a few more. I have not seen their codes, so I don’t know whether they are a good one or not- but it exists anyway (!) and may be useful someday. Thanks to Saeed for the link (he does not have a site nowadays).