Stack.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace DataStructSandBox.DataStructures
{

    public interface IStack<T>{

        int Size();

        bool IsEmpty();

        T Pop();

        void Push(T data);

        T Top();


    }

    class Stack<T> : IStack<T>, IEnumerable
    {
       private  LinkedList<T> ll = new LinkedList<T>();

        public Stack()
        {

        }

        public int Size() => this.ll.Count;

        public bool IsEmpty() => this.ll.Count == 0;

        public T Pop()
        {
            if (this.IsEmpty())
                throw new NullReferenceException();
            T data = this.ll.First.Value;
            this.ll.RemoveFirst();
            return data;
        }

        public void Push(T data)
        {
            this.ll.AddFirst(data);
        }

        public T Top()
        {
            return this.ll.First.Value;
        }

        public IEnumerator GetEnumerator() => this.ll.GetEnumerator();
    }

    // driver 
    public class Program
    {
        public static int Main()
        {
            Stack<int> st = new Stack<int>();

            st.Push(1);
            st.Push(8);
            st.Push(6);
            st.Push(7);

            foreach (int i in st)
            {
                Console.Write("{0} ", i);
            }

            // output: 7 6 8 1
            // last value is at the top

            return 0;
        }
    }
}