Compilare: user.cpp: In function ‘void DFs(const int&)’: user.cpp:41:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < Sons.size() ; i += 2) { ^ user.cpp: In function ‘int main()’: user.cpp:58:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < Ans.size() ; ++ i) ^