foo.cc: In function ‘std::string tran(int, int)’:
foo.cc:16:9: error: ‘reverse’ was not declared in this scope
   16 |         reverse(ans.begin(), ans.end());
      |         ^~~~~~~
foo.cc: In function ‘int main()’:
foo.cc:25:27: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   25 |         for (int i = 0; i < num.size(); i++)
      |                         ~~^~~~~~~~~~~~