佇列記住的是back的地址

構造時back指向back，表示空佇列；

#include<iostream>
#include<ctime>//...
#include<stdlib.h>//隨機數要的


using namespace std;

template<typename T>
class listNode//只是一個節點
{
public:
	T NodeData;
	listNode *next;
	listNode(T data, listNode * ne){ NodeData = data; next = ne; }
	listNode(){ NodeData = NULL; next = NULL; }
};




template<typename T>
class Queue
{
public:
	Queue();
	Queue(const  Queue<T> & or);
	void enqueue(const T & item);//
	void dequeue();//
	const T & front() const;
	bool empty() const;//
	void display() const;
	Queue & operator =(const Queue<T> &or);
	~Queue();
private:
	listNode<T>* myBack;
};

template<typename T>
Queue<T>::Queue(){ myBack = new listNode<T>(); myBack->next = myBack; }//這個myback已經成了最簡單的迴圈列表，指向它自己，這個myback都是留著不放東西的，也將是是否為空的判斷依據！


template<typename T>
Queue<T>::Queue(const  Queue<T>& or)
{ 
	myBack = new listNode<T>();
	myBack->next = myBack;
	listNode<T> *pr = or.myBack->next,*pt=myBack->next;
	myBack->NodeData = or.myBack->NodeData;
	myBack->next = myBack;

	while (pr !=or.myBack)
	{
		pt = new listNode<T>(NULL, myBack->next);
		myBack->NodeData = pr->NodeData;
		myBack->next = pt;
		myBack = pt;
		pr = pr->next;
	}


}


template<typename T>
Queue<T>::~Queue()
{ 
	listNode<T> *pr=myBack->next,*pt; 
	while (pr != myBack)
	{
		pt = pr->next;
		delete pr;
		pr = pt;
	}
}

template<typename T>
void Queue<T>::enqueue(const T & item)//新增咯，感覺是除了構造最重要的函式
{ //這裡是這樣的：先新建一個節點記住myback的next，這樣才能保證是個迴圈的圈~（因為最後這個節點會變成myback）；
	listNode<T> *pr;
	pr = new listNode<T>(NULL, myBack->next);//記住myback的下一個就是第一個的地址；
	myBack->NodeData = item;//把要新增的節點的值賦給當前的最後一個；
	myBack->next = pr;//指向新節點，將是新的myback;
	myBack = pr;//這樣myback就後移了
}//其實就是將新節點插在myback前面，而且沒有遍歷連結串列。


template<typename T>
bool Queue<T>::empty() const  { return myBack == myBack->next; }//就和剛構造的時候一樣，當就剩下一個myback的時候哦就是空了；


template<typename T>
void Queue<T>::dequeue()//刪除第一個節點。也就是myback間隔跳了一個，然後哦把跳過的那一個的空間給還了；
{
	listNode<T> *pr;
	try
	{
		if (empty())//先判斷是不是空的，空的不能刪，給它報錯
			throw out_of_range("Queue<>::dequeue() :empty queue");
		else
		{
			pr = myBack->next;//pr記住myback的next（其實就是第一個了），為了跳過第一個有了第二句。。
			myBack->next = pr->next;//跳過了
			delete pr;//還空間
		}
		
	}
	catch (exception const& ex)//抓異常的
	{
		cerr << "Exception: " << ex.what() << endl;
	}

}


template<typename T>
const T & Queue<T>::front() const
{
	listNode<T> *pr;
	pr = myBack->next;
	
	try
	{
		if (empty())
			throw out_of_range("Queue<>::dequeue() :empty queue");
		else
			return pr->NodeData;

	}
	catch (exception const& ex)
	{
		cerr << "Exception: " << ex.what() << endl;
	}

}


template<typename T>
void Queue<T>::display() const
{
	listNode<T> *pr=myBack->next;
	if (empty())
	{
		cout << "Queue<>::dequeue() :empty queue\n";
		return;
	}
	while (pr!=myBack)
	{
		cout << pr->NodeData<<" ";
		pr = pr->next;
	}
	cout << endl;
}

template<typename T>
Queue<T> & Queue<T>::operator =(const Queue<T> &or)
{
	Queue<T>::~Queue();
	myBack = new listNode<T>();
	myBack->next = myBack;
	listNode<T> *pr = or.myBack->next, *pt = myBack->next;
	myBack->NodeData = or.myBack->NodeData;
	myBack->next = myBack;

	while (pr != or.myBack)
	{
		pt = new listNode<T>(NULL, myBack->next);
		myBack->NodeData = pr->NodeData;
		myBack->next = pt;
		myBack = pt;
		pr = pr->next;
	}
	return *this;
}
 

#include"Queue.h"

using namespace std;

int main()
{
	Queue<int> que;
	int i = 1;
	int num;
	srand(unsigned int(time(0)));
	cout << "隨機產生的從0~99的數字20個：" << endl;
	for (; i <= 20; i++)
	{
		num = rand() % 100;
		cout << num << " ";
		que.enqueue(num);
	}
	cout << endl<<endl<<endl;
	system("pause");
	que.display();
	system("pause");

	Queue<int> que2(que), que3 = que;
	//que2.display();
	//que3.display();
	//system("pause");
	cout << "開始刪除\n";
	while (!que.empty())
	{
		cout << que.front() <<endl;
		que.dequeue();
	}
	cout << endl;
	system("pause");
	que.dequeue();
	system("pause");
	que.display();
	system("pause");
	cout<<que.front();
	system("pause");

	cout << "que2 以及que3 未被刪\n";
	que2.display();
	que3.display();
	system("pause");


	return 0;
}