using System;

public class Program

{

    public class Stack<T>

    {

        private class Element {

            public Element Next;

            public int? Index;

            public T Value;

            public Element() { Next = null; Value = default(T); Index = null; }

            public Element(T v, int i) { Value = v; Index = i; }

            public Element(Element item)

            {

                Index = item.Index;

                Value = item.Value;

                if (item.Next != null)

                    Next = new Element(item.Next);

                else Next = null;

            }

        }

        private int _Count;

        private Element _Items;

        public int Count { get { return _Count; } }

        private T GetElem(int ind)

        {

            Element Temp = new Element(_Items); 

            while (Temp != null)

            {

                if (Temp.Index == ind) break;

                Temp = Temp.Next;

            }

            return Temp.Value;

        }

        private void SetElem(int ind, T value)

        {

            Element Temp = new Element(_Items);

            Element Final = new Element();

        }

        public T this[int index]

        {

            get { 

                if (index < 0 || index >= Count)

                    throw new Exception("Index out of array bounds.");

                return GetElem(index);

            }

            set { 

                if (index < 0 || index >= Count)

                    throw new Exception("Index out of array bounds.");

                SetElem(index, value);

            }

        }

        public void Add(T value)

        {

            if (_Items == null) _Items = new Element(value, _Count); 

            else

            {

                _Items.Next = new Element(_Items); 

                _Items.Value = value; 

                _Items.Index = _Count; 

            }

            ++_Count;

        }

        public int IndexOf(T value) 

        {

            Element Temp = new Element(_Items);

            while (Temp != null)

            {

                if (Temp.Value.Equals(value)) break;

                Temp = Temp.Next;

            }

            return (int)Temp.Index; 

        }

        public Stack() { _Count = 0; _Items = null; }

    }

    public static void Main()

    {

        Stack<int> stack = new Stack<int>();

        stack.Add(531);

        stack.Add(2235);

        stack.Add(678);

        Console.WriteLine("Count       : " + stack.Count);

        Console.WriteLine(stack[0]);

        //stack[0] = 200;

        Console.WriteLine(stack[0]);

        Console.WriteLine("IndexOf 531 : " + stack.IndexOf(531));

    }

}