/in/foo.cc: In function 'void change(std::string&)':
/in/foo.cc:6:19: 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:22:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |   for (int i = 0;i <= num1.length()-1;i++)
      |                  ~~^~~~~~~~~~~~~~~~~~