c++队列

// MyQueue.cpp : 定义控制台应用程序的入口点。
//实现链式队列（queue），包括一个头结点。队列操作包括在队头出队（pop）、在队尾入队（push）、
//取得队头元素（front_element)、取得队尾元素（back_element）、队列元素个数（size）、
//队列是否为空（empty）。
#include "stdafx.h"
#include <iostream>


using namespace std;


//定义队列的节点结构
template <class T>
struct NODE
{
NODE<T>* next;
T data;
};


template <class T>
class MyQueue
{
public:
MyQueue()
{
NODE<T>* p = new NODE<T>;
if (NULL == p)
{
cout << "Failed to malloc the node." << endl;
}
p->data = NULL;
p->next = NULL;
front = p;
rear = p;
}


//在队尾入队
void push(T e)
{
NODE<T>* p = new NODE<T>;
if (NULL == p)
{
cout << "Failed to malloc the node." << endl;
}
p->data = e;
p->next = NULL;
rear->next = p;
rear = p;
}


//在队头出队
T pop()
{
T e;


if (front == rear)
{
cout << "The queue is empty." << endl;
return NULL;
}
else
{
NODE<T>* p = front->next;
front->next = p->next;
e = p->data;
//注意判断当只有一个元素，且删除它之后，rear指向的node被删除
//应将其指向头结点
if (rear == p)
{
rear = front;
}
delete p; p = NULL;
return e;
}
}


//取得队头元素
T front_element()
{
if (front == rear)
{
cout << "The queue is empty." << endl;
return NULL;
}
else
{
NODE<T>* p = front->next;
return p->data;
}
}


T back_element()
{
if (front == rear)
{
cout << "The queue is empty." << endl;
return NULL;
}
else
{
return rear->data;
}
}

//取得队列元素个数
int size()
{
int count(0);


NODE<T>* p = front;


while (p != rear)
{
p = p->next;
count++;
}
return count;
}

//判断队列是否为空
bool empty()
{
if (front == rear)
{
return true;
}
else
{
return false;
}
}


private:
NODE<T>* front; //指向头结点的指针。 front->next->data是队头第一个元素。
NODE<T>* rear;//指向队尾（最后添加的一个元素）的指针
};


int _tmain(int argc, _TCHAR* argv[])
{
MyQueue<int> myqueue;
cout << myqueue.size() << endl;
myqueue.push(10);
myqueue.push(20);
myqueue.push(30);
cout << myqueue.front_element() << endl;
cout << myqueue.back_element() << endl;
myqueue.pop();
if (myqueue.empty())
{
cout << "The queue is empty now." << endl;
}
else
{
cout << "The queue has " << myqueue.size() << " elements now." << endl;
}
myqueue.pop();
myqueue.pop();
if (myqueue.empty())
{
cout << "The queue is empty now." << endl;
}
else
{
cout << "The queue has " << myqueue.size() << " elements now." << endl;
}
return 0;
}