foo.cc: In function ‘bool judge(std::string)’:
foo.cc:75:27: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   75 |         for (int i = 0; i < s.size(); i++)
      |                         ~~^~~~~~~~~~
foo.cc: In function ‘std::string div(std::string, std::string, int)’:
foo.cc:72:1: warning: control reaches end of non-void function [-Wreturn-type]
   72 | }
      | ^