foo.cc: In function 'int main()':
foo.cc:18:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |     for(int i=0;i<s1.length();++i)
      |                 ~^~~~~~~~~~~~
foo.cc:25:15: 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 i=0;i<s2.length();++i)
      |              ~^~~~~~~~~~~~

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