Стек

Stack<string> numbers = new Stack<string>(); 

numbers.Push("one"); 

numbers.Push("two"); 

numbers.Push("three"); 

// Peek()

// Pop()

using System.Collections;

Stack myStack = new Stack();

myStack.Push(textBox1.Text);

if (myStack.Count > 0)

{

      richTextBox1.Text = myStack.Pop().ToString();

}