/in/foo.cc: In function 'int main()':
/in/foo.cc:9:32: error: 'reverse' was not declared in this scope
  reverse(str.begin(), str.end());
                                ^
/in/foo.cc:10:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < str.size(); i++)
                  ~~^~~~~~~~~~~~
/in/foo.cc:15:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = flag; i < str.size(); i++)
                      ~~^~~~~~~~~~~~