/in/foo.cc: In function 'int main()':
/in/foo.cc:18:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<a.size(); ++i) top[i]=abs(a[i]-b[i]);
                ~^~~~~~~~~
/in/foo.cc:21:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (top[x]>0 && x<a.size()) x++;
                     ~^~~~~~~~~