/in/foo.cc: In function 'int main()':
/in/foo.cc:12:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0, j = str.size() - 1; i < str.size(), j >= 0; i++, j--)
                                      ~~^~~~~~~~~~~~
/in/foo.cc:12:40: warning: value computed is not used [-Wunused-value]
/in/foo.cc:32:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < str.size(); i++)
                  ~~^~~~~~~~~~~~