# include <deque>
# include <algorithm>

int main() {
   std::deque<int> a3_deq(10);
   std::cout << "Сoдержимое " << std::endl;
   std::copy(a3_deq.begin(), a3_deq.end(), std::ostream_iterator<int>(std::cout, " "));

   return 0;
}

Сoдержимое 
0 0 0 0 0 0 0 0 0 0