foo.cc: In function 'int main()':
foo.cc:14:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   14 |                 for (i = 0; i < S.length(); i++) {
      |                             ~~^~~~~~~~~~~~
foo.cc:24:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |                 if (i == S.length())
      |                     ~~^~~~~~~~~~~~~
foo.cc:27:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |                         for (; i < S.length(); i++) {
      |                                ~~^~~~~~~~~~~~
foo.cc:33:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |                         if (i == S.length())
      |                             ~~^~~~~~~~~~~~~

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