foo.cc: In function 'int main()':
foo.cc:9:14: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |     for(i=1;i<=s1.size();i++)
      |             ~^~~~~~~~~~~
foo.cc:13:11: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |  for(i=1;i<=s2.size();i++)
      |          ~^~~~~~~~~~~

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