foo.cc: In function 'int main()':
foo.cc:33:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |   for(int i=0;i<s.size();i++)
      |               ~^~~~~~~~~
foo.cc:35:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   35 |   for(int i=0;i<s.size()-1;i++)
      |               ~^~~~~~~~~~~
foo.cc:53:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   53 |  for(int i=0;i<res.size();i+=2) ans[len++]=res.substr(i,2);
      |              ~^~~~~~~~~~~

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