/in/foo.cc: In function 'void change(std::string&)':
/in/foo.cc:6:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    6 |  for (int i = 0; i < s.length()/2; i++)
      |                  ~~^~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:52:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   52 |       for (int i = n / 2; i < num.length(); i++)
      |                           ~~^~~~~~~~~~~~~~
/in/foo.cc:76:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   76 |       for (int i = n / 2; i < num.length(); i++)
      |                           ~~^~~~~~~~~~~~~~