foo.cc: In function ‘int CountUpper(std::string&)’:
foo.cc:13:22: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   13 |         for(int i=0;i<s.length();i++)
      |                     ~^~~~~~~~~~~
foo.cc: In function ‘int CountLower(std::string&)’:
foo.cc:21:22: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   21 |         for(int i=0;i<s.length();i++)
      |                     ~^~~~~~~~~~~