/in/foo.cc: In function 'int duand(std::__cxx11::string, std::__cxx11::string, int)':
/in/foo.cc:8:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<s.length() && j<t.length())
        ~^~~~~~~~~~~
/in/foo.cc:8:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<s.length() && j<t.length())
                        ~^~~~~~~~~~~
/in/foo.cc:15:6: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(j>=t.length())
     ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:37:6: warning: unused variable 'si' [-Wunused-variable]
  int si=0;
      ^~