/in/foo.cc: In function 'int main()':
/in/foo.cc:31:23: 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> >]'
             output = {};
                       ^
/in/foo.cc:31:23: note: in C++11 and above a default constructor can be explicit