/in/foo.cc: In function 'int main()':
/in/foo.cc:24:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int len=1;len<=str.size();len++)
                ~~~^~~~~~~~~~~~
/in/foo.cc:27:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int l=0;l+len<=str.size();l+=len)
               ~~~~~^~~~~~~~~~~~
/in/foo.cc:30:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(l+len==str.size())
       ~~~~~^~~~~~~~~~~~