/in/foo.cc: In function 'bool check0(std::__cxx11::string)':
/in/foo.cc:29:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 1; i < str.size() - 2; i++)
                  ~~^~~~~~~~~~~~~~~~
/in/foo.cc: In function 'bool check1(std::__cxx11::string)':
/in/foo.cc:39:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 1; i < str.size() - 2; i++)
                  ~~^~~~~~~~~~~~~~~~