int freqs[256]={0};

I think that syntax is part of C99, inherited back as a "good idea" from C++. If the initializer list in curly brackets is shorter than the number of elements in the entity being initialized, all elements not enumerated in the list will initialize to zero. Ex: int freqs[256]={1}; would initialize as freqs[0] = 1, freqs[1] = 0, freqs[2] = 0, etc.

gcc offers some additional features beyond that, but the syntax used here should be portable to any C99 implementation.