Compilare: main.cpp: In function 'Result eval(const string&, size_t)': main.cpp:22:30: warning: converting to 'std::queue<char>' from initializer list would use explicit constructor 'std::queue<_Tp, _Sequence>::queue(_Sequence&&) [with _Tp = char; _Sequence = std::deque<char, std::allocator<char> >]' queue<char> op[2] = {{}, {}}; // + or - ^ main.cpp:22:30: note: in C++11 and above a default constructor can be explicit main.cpp:22:30: warning: converting to 'std::queue<char>' from initializer list would use explicit constructor 'std::queue<_Tp, _Sequence>::queue(_Sequence&&) [with _Tp = char; _Sequence = std::deque<char, std::allocator<char> >]' main.cpp:22:30: note: in C++11 and above a default constructor can be explicit main.cpp:24:30: warning: converting to 'std::queue<int>' from initializer list would use explicit constructor 'std::queue<_Tp, _Sequence>::queue(_Sequence&&) [with _Tp = int; _Sequence = std::deque<int, std::allocator<int> >]' queue<int> num[2] = {{}, {}}; ^ main.cpp:24:30: note: in C++11 and above a default constructor can be explicit main.cpp:24:30: warning: converting to 'std::queue<int>' from initializer list would use explicit constructor 'std::queue<_Tp, _Sequence>::queue(_Sequence&&) [with _Tp = int; _Sequence = std::deque<int, std::allocator<int> >]' main.cpp:24:30: note: in C++11 and above a default constructor can be explicit