Compilare: user.cpp: In member function ‘void FFT::reverse_by_bits(std::vector<std::complex<long double> >&)’: user.cpp:14:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (lg = 0; (1<<lg) < v.size(); lg++); ~~~~~~~~^~~~~~~~~~ user.cpp:18:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < v.size(); i++) { ~~^~~~~~~~~~ user.cpp:23:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size(); i++) { ~~^~~~~~~~~~ user.cpp: In member function ‘std::vector<std::complex<long double> > FFT::mul(std::vector<std::complex<long double> >, std::vector<std::complex<long double> >)’: user.cpp:64:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < c.size(); i++) c[i] = a[i] * b[i]; ~~^~~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:100:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) { ~~^~~~~~~~~~ user.cpp:108:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < b.size(); i++) { ~~^~~~~~~~~~ user.cpp:78:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("stradacramei.in", "r", stdin); ^ user.cpp:79:43: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("stradacramei.out", "w", stdout); ^