foo.cc: In function ‘int TD(std::string, int)’:
foo.cc:9:29: warning: comparison of integer expressions of different signedness: ‘long long int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
    9 |     for (long long i = 0; i < num.size(); i++)
      |                           ~~^~~~~~~~~~~~