/in/foo.cc: In function 'int main()':
/in/foo.cc:12:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < a.size(); i++)cout << a[i];
                  ~~^~~~~~~~~~
/in/foo.cc:17:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < b.size(); i++)cout << b[i];
                  ~~^~~~~~~~~~
/in/foo.cc:19:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < a.size(); i++)cout << a[i];
                  ~~^~~~~~~~~~
/in/foo.cc:21:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < b.size(); i++)cout << b[i];
                  ~~^~~~~~~~~~
/in/foo.cc:24:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < b.size(); i++)cout << b[i];
                  ~~^~~~~~~~~~
/in/foo.cc:29:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < a.size(); i++)cout << a[i];
                  ~~^~~~~~~~~~