/in/foo.cc: In function 'std::__cxx11::string Mul(const string&, int)':
/in/foo.cc:18:39: error: too many arguments to function 'int to_string()'
         result += to_string(total % 10);
                                       ^
/in/foo.cc:10:6: note: declared here
  int to_string(); 
      ^~~~~~~~~
/in/foo.cc:22:39: error: too many arguments to function 'int to_string()'
         result += to_string(carry % 10);
                                       ^
/in/foo.cc:10:6: note: declared here
  int to_string(); 
      ^~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:49:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (space_pos == string::npos) 
         ~~~~~~~~~~^~~~~~~~~