foo.cc: In function 'int main()':
foo.cc:23:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i != num1.size() && j != num2.size())
         ~~^~~~~~~~~~~~~~
foo.cc:23:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i != num1.size() && j != num2.size())
                             ~~^~~~~~~~~~~~~~
foo.cc:44:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (i != num1.size())
         ~~^~~~~~~~~~~~~~
foo.cc:49:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while (j != num2.size())
         ~~^~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。