Compilare: user.cpp: In function ‘bool exp(std::string)’: user.cpp:25:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0; j<=out.size(); ++j) ^ user.cpp: In function ‘int main()’: user.cpp:50:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<s.size();++i) ^