20     std::stack<int> q;  in main()  local
21     assert(q.size() == 0);  in main()
22     q.push(1);  in main()
23     q.push(2);  in main()
24     q.push(3);  in main()
25     assert(q.size() == 3);  in main()
26     assert(q.top() == 3);  in main()
27     q.pop();  in main()
28     assert(q.size() == 2);  in main()
29     assert(q.top() == 2);  in main()
30     q.pop();  in main()
31     assert(q.size() == 1);  in main()
32     assert(q.top() == 1);  in main()
33     q.pop();  in main()
34     assert(q.size() == 0);  in main()