/in/foo.cc: In function 'int main()':
/in/foo.cc:48:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
      for (int j = n.s.find(a[i]); j <= n.s.length()-a[i].length(); j = n.s.find(a[i], j+1))
                                   ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~