/in/foo.cc: In function 'int main()':
/in/foo.cc:16:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |   for (i = 0; i < s.length() && flag; i++)
      |               ~~^~~~~~~~~~~~
/in/foo.cc:18:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |    for (j = 0; j < s.length(); j++)
      |                ~~^~~~~~~~~~~~
/in/foo.cc:21:10: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |    if (j == s.length())
      |        ~~^~~~~~~~~~~~~
/in/foo.cc:29:3: error: 'reverse' was not declared in this scope
   29 |   reverse(s.begin(), s.end());
      |   ^~~~~~~
/in/foo.cc:31:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   31 |   for (i = 0; i < s.length() && flag; i++)
      |               ~~^~~~~~~~~~~~
/in/foo.cc:33:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |    for (j = 0; j < s.length(); j++)
      |                ~~^~~~~~~~~~~~
/in/foo.cc:36:10: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |    if (j == s.length())
      |        ~~^~~~~~~~~~~~~