foo.cc: In function 'bool check()':
foo.cc:35:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   35 | for (int k = 0; k < s.size(); k++)
      |                 ~~^~~~~~~~~~
foo.cc:39:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 | for (int k = 0; k < s.size(); k++)
      |                 ~~^~~~~~~~~~

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