1. void enqueue(int)：將某個值的元素放入佇列的尾部 (tail)，

3. bool is_empty()：測試佇列是否為空的。

1. 將某個值的元素放入佇列的尾部，

2. 將佇列的頭部的元素移出，並印出該元素的值

3. 測試佇列是否為空的，

4. 從頭部至尾部列印佇列中所有元素的值

5. 終止程式執行。

 **************************************** 　 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 1 Input the element being enqueued: 50 　 **************************************** 1. Enqueue an elemnet to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 1 Input the element being enqueued: 48 **************************************** 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 1 Input the element being enqueued: 24 **************************************** 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 1 Input the element being enqueued: 60 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program **************************************** Input command: 4 The queue elements are (from head to tail):     50     48     24     60 **************************************** 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 2 The dequeued element: 50 **************************************** 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 3 The queue is not empty. **************************************** 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 4 The queue elements are (from head to tail):     48     24     60 **************************************** 1. Enqueue an element to the queue 2. Dequeue an element from the queue 3. Test empty queue 4. Print queue elements 5. Exit the program Input command: 5