/in/foo.cc: In function 'int main()':
/in/foo.cc:7:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    7 |         for (int len=2;len<=s.size();len++)
      |                        ~~~^~~~~~~~~~
/in/foo.cc:9:41: 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 l=0,r=l+len-1;r<s.size();l++,r++)
      |                                        ~^~~~~~~~~