Compilare: user.cpp: In function ‘void fft(std::vector<std::complex<double> >&, int)’: user.cpp:25:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < p.size(); ++i) ^ user.cpp:31:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < p.size() / 2; ++i) { ^ user.cpp: In function ‘int main()’: user.cpp:60:22: warning: suggest parentheses around ‘-’ in operand of ‘&’ [-Wparentheses] for (++mx; mx & mx - 1; mx++); ^