Compilare: user.cpp: In function ‘void mult()’: user.cpp:49:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<A.size();i++) _C[i] = A[i] * B[i]; ~^~~~~~~~~ user.cpp:52:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<A.size();i++) C[i] = _C[i].real() + 0.5; ~^~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:76:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<C.size();i++) if (C[i]) g<<i<<' '<<C[i]<<'\n'; ~^~~~~~~~~