foo.cc: In function ‘int main()’:
foo.cc:9:14: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
    9 | for(int i=0;i<s1.size();i++)
      |             ~^~~~~~~~~~
foo.cc:12:14: 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<s2.size();i++)
      |             ~^~~~~~~~~~