/in/foo.cc: In function 'int main()':
/in/foo.cc:9:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0,j=0;i<b.length();++i,++j){
                  ~^~~~~~~~~~~
/in/foo.cc:10:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(j==a.length())
      ~^~~~~~~~~~~~