foo.cc: In function 'int main()':
foo.cc:12:15: 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<s1.size() ;i++)
      |              ~^~~~~~~~~~

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