foo.cc: In function 'int main()':
foo.cc:9:32: 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(long long int i=0;i<s.size();i+=2)
      |                               ~^~~~~~~~~
foo.cc:22:26: 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]
   22 |                 else if(i<s.size())
      |                         ~^~~~~~~~~

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