I did my CNN implementation in C++ a couple of years back using this: http://cs231n.stanford.edu http://cs231n.stanford.edu Around 600 lines of free functions

I did my CNN implementation in C++ a couple of years back using this: http://cs231n.stanford.edu http://cs231n.stanford.edu Around 600 lines of free functions in a header file for the core functionality, including convolution, dropout, batch normalization, etc. Maybe half of it is actual code. Around 2000 lines for an executable training program including a couple of array template classes, data loaders, and convenience functions. Slow as shit but it works :P An enjoyable exercise.