/in/foo.cc: In function 'void add()':
/in/foo.cc:12:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i < A.size() && i < B.size()) {
         ~~^~~~~~~~~~
/in/foo.cc:12:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i < A.size() && i < B.size()) {
                         ~~^~~~~~~~~~
/in/foo.cc:18:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i < A.size()) {
         ~~^~~~~~~~~~
/in/foo.cc:24:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i < B.size()) {
         ~~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:37:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < a.size(); i++) {
                  ~~^~~~~~~~~~
/in/foo.cc:40:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < b.size(); i++) {
                  ~~^~~~~~~~~~