Link stack C++

#include<iostream>
using namespace std;
 
class Node
{
private:
    int data;
    Node* next;
public:
    void push(int x);
    int pop();
    void Display();
}*top=NULL;
void Node::push(int x)
{
    Node* t = new Node;
    if (t == NULL)
        cout << "pull stack";
    t->data = x;
    t->next = top;
    top = t;
}
int Node::pop()
{
    Node* t = top;
    int x = -1;
    if (top == NULL)
        cout << "empty";
    else
    {
        x = t->data;
        top = top->next;
        delete t;
    }
    return x;
}
void Node::Display()
{
    Node* t = top;
    while (t)
    {
        cout << t->data << " ";
        t = t->next;
    }
}
int main()
{
    Node s;
    s.push(10);
    s.push(20);
    s.push(30);
    cout << s.pop()<<endl;
    s.Display();
    return 0;
}