iterator pattern in C++

```
#include <iostream>
using namespace std;

class StackIter;

class Stack
{
    int items[10];
    int sp;
public:
    Stack() {
        sp =  - 1;
    }
    void push(int in) {
        items[++sp] = in;
    }
    int pop() {
        return items[sp--];
    }
    bool isEmpty() {
        return (sp ==  - 1);
    }
    friend class StackIter;
    StackIter *createIterator()const; // 2. Add a createIterator() member
};

class StackIter
{
    const Stack *stk;
    int index;
  public:
    StackIter(const Stack *s) {
        stk = s;
    }
    void first() {
        index = 0;
    }
    void next() {
        index++;
    }
    bool isDone() {
        return index == stk->sp + 1;
    }
    int currentItem() {
        return stk->items[index];
    }
};


StackIter *Stack::createIterator()const
{
  return new StackIter(this);
}


bool operator == (const Stack &l, const Stack &r)
{
  StackIter *itl = l.createIterator();
  StackIter *itr = r.createIterator();

  for (itl->first(), itr->first(); !itl->isDone(); itl->next(), itr->next())
    if (itl->currentItem() != itr->currentItem())
      break;
  bool ans = itl->isDone() && itr->isDone();
  delete itl;
  delete itr;
  return ans;
}

int main()
{
  Stack s1;
  for (int i = 1; i < 5; i++)
    s1.push(i);
  Stack s2(s1), s3(s1), s4(s1), s5(s1);
  s3.pop();
  s5.pop();
  s4.push(2);
  s5.push(9);

  cout << "1 == 2 is " << (s1 == s2) << endl;
  cout << "1 == 3 is " << (s1 == s3) << endl;
  cout << "1 == 4 is " << (s1 == s4) << endl;
  cout << "1 == 5 is " << (s1 == s5) << endl;
}

/*
1 == 2 is 1
1 == 3 is 0
1 == 4 is 0
1 == 5 is 0
*/

```
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