Stack using Class,Array and Pointer

#include<iostream>
using namespace std;

class stack
{
 public:    
 stack(int num){
  top=-1;
  max=num;
  a=new int[max];
 };  
 void push();
 void pop();
 void display();
private:
int top;
int max;
int input;
int *a;

 };

 void stack::push()
{
 if(top==max-1)
 {
  cout<<"stack is overflow"<<endl;
 }
 else
 {
  cout<<"Enter the Element in the Stack"<<endl;
  cin>>input;
  top=top+1;
  a[top]=input;
 }
 }

 void stack::pop()
{
 if(top==-1)
 {
 cout<<"Stack is Empty"<<endl;
 }
 else
 {
 cout<<"Stack value : "<<a[top]<<endl;
 top=top-1;
 }
}

void stack::display()
{
if(top==-1)
 {
 cout<<"Stack is Empty"<<endl;
 }
 else
 {for(int i=top; i>=0; i--)
 {
  cout<<"Stack["<<i<<"] : "<<a[i]<<endl;
 }
 }
}

int main()
{
int data;
cout<<"Enter the max len of Stack"<<endl;
cin>>data;
stack *stk=new stack(data);
int select;
char again;
do{
  cout<<"***** 1.PUSH ****"<<endl;
  cout<<"***** 2.POP ****"<<endl;
  cout<<"***** 3.Display ****"<<endl;
  cout<<"Select the option"<<endl;
  cin>>select;
switch(select)
 {
 case 1:stk->push();break;
 case 2:stk->pop(); break;
 case 3:stk->display();break;
 default : cout<<"Wrong input"<<endl;
}
cout<<"Do You Want Again(Y/N)"<<endl;
cin>>again;
}while(again=='y'||again=='Y');
}

output :

* note :

int *array = new int[n];

It declares a pointer to a dynamic array of type int and size n.
A little more detailed answer: new allocates memory of size equal to sizeof(int) * n bytes and return the memory which is stored by the variable array. Also, since the memory is dynamically allocated using new