Compilare: user.cpp: In function ‘bool valid(std::vector<int>)’: user.cpp:18:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<vec.size();i++){ ^ user.cpp: In function ‘int main()’: user.cpp:41:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<str.size();i++){ ^ user.cpp:52:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<one.size();j++) ^ user.cpp:56:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<two.size();j++) ^