View Compilation Error

0_0_38269064_6368.cpp: In function 'int main()':
0_0_38269064_6368.cpp:67:7: error: converting to 'std::stack<double>' from initializer list would use explicit constructor 'std::stack<_Tp, _Sequence>::stack(_Sequence&&) [with _Tp = double; _Sequence = std::deque<double, std::allocator<double> >]'
   num = {};
       ^
0_0_38269064_6368.cpp:68:6: error: converting to 'std::stack<char>' from initializer list would use explicit constructor 'std::stack<_Tp, _Sequence>::stack(_Sequence&&) [with _Tp = char; _Sequence = std::deque<char, std::allocator<char> >]'
   op = {};
      ^