/in/foo.cc: In function 'int main()':
/in/foo.cc:27:38: error: 'strrev' was not declared in this scope
  if (judge(s1, s2)) cout << strrev(s3) << endl;
                                      ^
/in/foo.cc:28:43: error: 'strrev' was not declared in this scope
  else if (judge(s1, s3)) cout << strrev(s2) << endl;
                                           ^
/in/foo.cc:29:24: error: 'strrev' was not declared in this scope
  else cout << strrev(s1) << endl;
                        ^