循环队列实现(C++)

循环队列：队列有着先入先出的特性。但是对于队列如果删除队头以后剩下的空间将不会被释放，又由于队列只能由队尾插入这就导致
被删除部分的空间被浪费。解决这个问题就是循环队列。循环队列顾名思义就是将队列串起来形成一个类似与环的结构。如图所示。对照着图很容易理解:
对于原来队列里的操作自然有不同的地方：
1.判断满：循环队列的满不再是rear=front 而是改成(rear-front+maxn)%maxn。
2.入队操作: data[rear] = x; rear = (rear+1)%maxn;

总体思想就是不让rear和front的值超过maxn的大小。于是就在rear和front自增时候模maxn。 

#include <iostream>
using namespace std;

const int maxn = 100;
template <class T>
class enqueue
{
    public:
        enqueue();
        bool empty();
        bool full();
        void push_elem(T x);
        void pop_elem();
        T get_front();
        int get_len();
        void showenqueue();
        ~enqueue();
    private:
        T *data;
        int rear;
        int front;
        int length;
};

template <class T>
enqueue<T>::enqueue()
{
    rear = 0;
    front = 0;
    data = new T[maxn];
    length = maxn;
}

template <class T>
enqueue<T>::~enqueue()
{
    delete []data;
}

template <class T>
int enqueue<T>::get_len()
{
    return (rear-front+length)%length;
}

template <class T>
bool enqueue<T>::empty()
{
    if (front == rear)
        return true;
    else
        return false;
}

template <class T>
bool enqueue<T>::full()
{
    if ((rear+1)%length == front)
        return true;
    else
        return false;   
}

template <class T>
void enqueue<T>::push_elem(T x)
{
    if (!full())
    {
        data[rear] = x;
        rear = (rear+1)%length;
    }
    else
    {
        cout << "queue is full" << endl;
    }
}

template <class T>
void enqueue<T>::pop_elem()
{
    if (!empty())
        front = (front+1)%length;
    else
        cout << "queue is empty" << endl;
}

template <class T>
T enqueue<T>::get_front()
{
    if (!empty())
        return data[front];
    else
        cout << "queue is full" << endl;
}

template <class T>
void enqueue<T>::showenqueue()
{
    int cnt = front;
    if (front > rear)
        rear += length;
    while (cnt <= rear-1)
    {
        cout << data[cnt] << " ";
        cnt++;
    }
    cout << endl;
}

int main ()
{
    enqueue<int>q;
    int n;
    cin >> n;
    for (int i = 0; i < n; i++)
    {
        q.push_elem(i+1);
    }
    q.showenqueue();
    cout << q.get_front() << endl;
    cout << q.get_len() << endl;
    q.pop_elem();
    q.pop_elem();
    q.push_elem(7);
    q.push_elem(6);
    q.showenqueue();
    cout << q.get_len() << endl;
    q.~enqueue();
    system("pause");
    return 0;
}