foo.cc: In function 'int main()':
foo.cc:25:43: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   25 |                         for (int j = 0; j < s.size(); j++)
      |                                         ~~^~~~~~~~~~

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