Compilare: main.cpp: In function 'std::vector<std::complex<double> > fft_inv(std::vector<std::complex<double> >&)': main.cpp:109:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<x.size();i++) ~^~~~~~~~~ main.cpp: In function 'int main()': main.cpp:158:9: warning: unused variable 'nr1' [-Wunused-variable] int nr1 = 0 , nr2 = 0; ^~~ main.cpp:158:19: warning: unused variable 'nr2' [-Wunused-variable] int nr1 = 0 , nr2 = 0; ^~~ main.cpp:130:37: warning: ignoring return value of 'size_t fread(void*, size_t, size_t, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fread (buff , 1 , 4000000 , fin); ^