20     std::queue<int> q;  in main()  local
21     q.push(1);  in main()
22     assert(q.size() == 1);  in main()
23     assert(q.front() == 1);  in main()
24     assert(q.back() == 1);  in main()
25     q.push(2);  in main()
26     assert(q.size() == 2);  in main()
27     assert(q.front() == 1);  in main()
28     assert(q.back() == 2);  in main()
29     q.push(3);  in main()
30     assert(q.size() == 3);  in main()
31     assert(q.front() == 1);  in main()
32     assert(q.back() == 3);  in main()