Stack ADT - Linked List Implementation

using System;

namespace Stack_Linked_List_Implementation
{
     class Stack
     {
         public class Node
        {
            public object item;
            public Node next;

            public Node() {
            }

            public Node(object item) {
               this.item = item;
            }
        }

        private int length;
        private Node top;

        public Stack()
        {
             length = 0;
             top = null;
        }

        public int Length
        {
            get { return length; }
        }

        public bool isEmpty()
        {
             return top == null;
        }

        public void push(Object item)
        {
             length++;
             top = new Node()
             {
                  next = top,
                  item = item
             };
        }

        public Object pop()
        {
             Object item = "";
             if (!isEmpty())
             {
                  item = top.item;
                  top = top.next;
                  length--;
             }
             else
             {
                  Console.WriteLine("Error! Stack Underflow");
             }
             return item;
        }

        public Object peek()
        {
             Object item = "";
             if (!isEmpty())
             {
                  item = top.item;
             }
             else
             {
                  Console.WriteLine("Error! Stack Underflow");
             }
             return item;
        }

     }
}
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Driver Program Using Stack Class


using System;

namespace Stack_Linked_List_Implementation
{
     class Program
     {
          static void Main(string[] args)
          {
               Stack stack = new Stack();
               stack.push("Apple");
               stack.push("Banana");
               stack.push("Guava");           

               Console.WriteLine(stack.pop());
               Console.WriteLine(stack.peek());
               stack.push("Grape");
               stack.push("Orange");
               stack.push("Lemon");
               Console.WriteLine(stack.pop());

               Console.WriteLine("\nPress any key to continue...");
               Console.ReadKey();
          }
     }
}