using System;

using System.Collections;

using System.Collections.Generic;

​

namespace MyStack

{

    public class MyEnumerator<T> : IEnumerator<T>

    {

        private int position;

        private MyStack<T> stack;

​

        public MyEnumerator(MyStack<T> stack)

        {

            this.stack = stack;

            position = stack.Count;

        }

​

        public T Current => stack[position];

​

        object System.Collections.IEnumerator.Current => stack[position];

​

        public bool MoveNext()

        {

            position--;

            return position >= 0;

        }

​

        public void Dispose()

        {

​

        }

        public void Reset()

        {

            position = stack.Count;

        }

    }

​

    public class MyStack<T> : IEnumerable<T>

    {

        private const int DEFAULT_SIZE = 10;

        private T[] array;

        private int top;

​

        public int Count => top;

​

        public MyStack()

        {

            array = new T[DEFAULT_SIZE];

            top = 0;

        }

​

        public MyStack<T> Push(T value)

        {

            if(top == array.Length)

            {

                T[] newArray = new T[array.Length * 2];

                Array.Copy(array, newArray, array.Length);

                array = newArray;

            }

​

            array[top++] = value;

            return this;

        }

​

        public T Peek()

        {

            if(top == 0)

            {

                throw new InvalidOperationException("Stack is empty");

            }

            return array[top - 1];

        }

​

        public T Pop()

        {

            if (top == 0)

            {

                throw new InvalidOperationException("Stack is empty");

            }

            return array[--top];

        }

​

        public IEnumerator<T> GetEnumerator()

        {

            return new MyEnumerator<T>(this);

        }

​

        IEnumerator IEnumerable.GetEnumerator()

        {

            return new MyEnumerator<T>(this);

        }

​

        public T this[int i]

        {

            get

            {

                if(i < 0 || i > this.Count)

                {

                    throw new IndexOutOfRangeException("Trying to reach non-existing element of Stack");

                }

                return array[i];

            }

        }

    }

​

    class Program

    {

        public static void Main()

        {

            Console.WriteLine("---My Stack---");

            var t = new MyStack<int>();

            t.Push(1).Push(1).Push(1).Push(2).Push(3).Push(4).Push(5).Push(6).Push(7).Push(8).Push(9).Push(10).Push(10).Push(10);

            foreach (var v in t)

            {

                Console.WriteLine(v);

            }

            Console.WriteLine($"\n{t.Pop()}\n{t.Pop()}\n{t.Peek()}\n");

            foreach (var v in t)

            {

                Console.WriteLine(v);

            }

            Console.WriteLine();

            t.Push(9).Push(10).Push(11);

            foreach (var v in t)

            {

                Console.WriteLine(v);

            }

​

            Console.WriteLine("\n\n");

​

            Console.WriteLine("---Out of the box Stack---");

            var p = new Stack<int>();

            for(int i = 1; i <= 10; i++)

            {

                p.Push(i);

            }

            foreach(var v in p)

            {

                Console.WriteLine(v);

            }

            Console.WriteLine($"\n{p.Pop()}\n{p.Pop()}\n{p.Peek()}\n");

            foreach (var v in p)

            {

                Console.WriteLine(v);

            }

            Console.WriteLine();

            p.Push(9);

            p.Push(10);

            p.Push(11);

            foreach (var v in p)

            {

                Console.WriteLine(v);

            }

        }

​

    }

}

​