/in/foo.cc: In function 'std::string Mul(std::string, std::string)':
/in/foo.cc:27:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |         for(int i=1;i<result.size();i++)
      |                     ~^~~~~~~~~~~~~~