foo.cc: In function ‘std::string toP(int, int)’:
foo.cc:30:9: error: ‘reverse’ was not declared in this scope
   30 |         reverse(res.begin(), res.end());
      |         ^~~~~~~
foo.cc: In function ‘std::string modP(std::string&, std::string&, int)’:
foo.cc:41:27: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   41 |         for (int i = 0; i < d.size(); i++)
      |                         ~~^~~~~~~~~~