/in/foo.cc: In function 'int main()':
/in/foo.cc:25:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i<a.size())
         ~^~~~~~~~~
/in/foo.cc:28:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j = 0; j < b.size(); j++)
               ~~^~~~~~~~~~
/in/foo.cc:36:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (j == b.size())
       ~~^~~~~~~~~~~
/in/foo.cc:39:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < a.size(); i++)
                  ~~^~~~~~~~~~