foo.cc: In function 'std::string Mul(std::string, int)':
foo.cc:8:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |     for (int i = 0; i < s.size(); ++i)
      |                     ~~^~~~~~~~~~
foo.cc:12:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |     for (int i = 0; i < s.size(); ++i)
      |                     ~~^~~~~~~~~~

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