c++循环队列模板类

#include 
using namespace std;

template<class elemType>
class stack {
public:
    virtual bool isEmpty()const = 0;
    virtual void push(const elemType &x) = 0;
    virtual elemType pop() = 0;
    virtual elemType top() const = 0;
    virtual ~stack() {}
};

template<class elemType>
class linkStack :public stack {
private:
    struct node {
        elemType data;
        node *next;
        node(const elemType &x, node *N = NULL) {
            data = x;
            next = N;
        }
        node() :next(NULL) {}
        ~node() {}
    };
    node *elem;
public:
    linkStack() { elem = NULL; }
    ~linkStack();
    bool isEmpty()const {
        return elem == NULL;
    }
    void push(const elemType &x) {
        node*tmp = new node(x,elem);
        elem = tmp->next;
        elem = tmp;
    }
    elemType pop() {
        node *tmp = elem;
        elemType x = tmp->data;
        elem = elem->next;
        delete tmp;
        return x;
    }
    elemType top()const {
        return elem->data;
    }
};

template<class elemType>
linkStack::~linkStack() {
    node *tmp;
    while (elem != NULL) {
        tmp = elem;
        elem = elem->next;
        delete[]tmp;
    }
}


int main() {
    linkStack<int> s;
    cout << s.isEmpty() << endl;
    for (int i = 0; i < 20; ++i)
        s.push(i);
    for (int i = 0; i < 20; ++i)
        cout << s.pop() << endl;
    return 0;
}