/in/foo.cc: In function 'std::string add(std::string, int)':
/in/foo.cc:7:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    7 |         for (int i = 0; i < s.size(); i++)
      |                         ~~^~~~~~~~~~
/in/foo.cc: In function 'std::string _add(std::string, int)':
/in/foo.cc:15:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |         for (int i = 0; i < s.size(); i++)
      |                         ~~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:42:9: error: 'reverse' was not declared in this scope
   42 |         reverse(s1.begin(),s1.end());
      |         ^~~~~~~