foo.cc: In function 'void ReverseWord(std::string&)':
foo.cc:21:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |         for (; i < s.length(); i++)
      |                ~~^~~~~~~~~~~~
foo.cc:23:36: error: 'isBD' was not declared in this scope
   23 |                 if (s[i] == ' ' || isBD(s[i]) == 1)
      |                                    ^~~~

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