/in/foo.cc: In function 'int main()':
/in/foo.cc:24:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < b.size(); i++)
                  ~~^~~~~~~~~~
/in/foo.cc:25:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int j = 0; j < a.size(); j++)
                  ~~^~~~~~~~~~
/in/foo.cc:30:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int j = 0; j < a.size(); j++)
                  ~~^~~~~~~~~~
/in/foo.cc:17:10: warning: unused variable 't' [-Wunused-variable]
  int nb, t;
          ^