自定义Stack< T>made with IEnumerable<和数组

我有这个问题，我一直想弄清楚。我试图使CustomStack像Stack一样，只实现Push(T)， Pop()， Peek()和Clear()方法。我得到了这段代码，我认为它是正确的，但是输出只显示了一半的数字。我认为这与push方法有关，但我看不出它有什么问题。

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;
namespace Enumerator
{
    class Program
    {
        static void Main(string[] args)
        {
            CustomStack<int> collection = new CustomStack<int>();
            for (int i = 0; i < 30; i++)
            {
                collection.Push(i);
                Console.WriteLine(collection.Peek());
            }
            collection.Push(23);
            foreach (int x in collection)
            {
                Console.WriteLine(collection.Pop());
            }
            Console.WriteLine("current", collection.Peek());
            Console.ReadKey();
        }
    }
    public class CustomStack<T> : IEnumerable<T>
    {
        private T[] arr;
        private int count;
        public CustomStack()
        {
            count = 0;
            arr = new T[5];
        }

        public T Pop()
        {
            int popIndex = count;
            if (count > 0)
            {
                count--;
                return arr[popIndex];
            }
            else
            {
                return arr[count];
            }
        }
        public void Push(T item)
        {
            count++;
            if (count == arr.Length)
            {
                Array.Resize(ref arr, arr.Length + 1);
            }
            arr[count] = item;

        }
        public void Clear()
        {
            count = 0;
        }
        public T Peek()
        {
            return arr[count];
        }
        public int Count
        {
            get
            {
                return count;
            }
        }
        public IEnumerator<T> GetEnumerator()
        {
            return new MyEnumerator(this);
        }
        IEnumerator IEnumerable.GetEnumerator()
        {
            return new MyEnumerator(this);
        }
        public class MyEnumerator : IEnumerator<T>
        {
            private int position;
            private CustomStack<T> stack;
            public MyEnumerator(CustomStack<T> stack)
            {
                this.stack = stack;
                position = -1;
            }
            public void Dispose()
            {
            }
            public void Reset()
            {
                position = -1;
            }
            public bool MoveNext()
            {
                position++;
                return position < stack.Count;
            }
            Object IEnumerator.Current
            {
                get
                {
                    return stack.arr[position];
                }
            }
            public T Current
            {
                get
                {
                    return stack.arr[position];
                }
            }
        }
    }
}