stack data structure

#include <iostream>
using namespace std;
# define size 100
class Stack{
    public:
    int top;
    int a[size];
    Stack() {top=-1;}

void push(int x){
    if(top>=(size-1)){
         cout<<"full stack"<<endl;
    }
    else{
        a[++top]=x;
        cout<<x<<"pushed into stack"<<endl;
    }
}
int pop(){
    if(top<0){
        cout<<"stack underflow";
        return 0;
    }
    else{
        int x=a[top--];
        return x;
    }
}
};
int main() {
    Stack s;
    s.push(1);
    s.push(2);
	s.push(3);
	s.push(4);
	cout<<s.pop()<<endl;
	cout<<s.pop()<<endl;
	return 0;
}