Eroare de compilare: user.cpp: In function ‘int main()’: user.cpp:41: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘std::string evaluate(int, int)’: user.cpp:84: warning: comparison between signed and unsigned integer expressions user.cpp:122: error: reference to ‘plus’ is ambiguous user.cpp:20: error: candidates are: comparison plus /usr/include/c++/4.4/bits/stl_function.h:135: error: template<class _Tp> struct std::plus user.cpp:122: error: reference to ‘plus’ is ambiguous user.cpp:20: error: candidates are: comparison plus /usr/include/c++/4.4/bits/stl_function.h:135: error: template<class _Tp> struct std::plus