/in/foo.cc: In function 'int main()':
/in/foo.cc:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=l.length();i++)
              ~^~~~~~~~~~~~
/in/foo.cc:11:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=1;j<=r.length();j++)
               ~^~~~~~~~~~~~