Listing 12.2: Supporting Undo in a Program Similar to an Etch A Sketch Toy

Listing12.2.cs

using System.Collections;
class Program
{
  // ...

  public void Sketch()
  {
      Stack path = new Stack();
      Cell currentPosition;
      ConsoleKeyInfo key;  // Added in C# 2.0

      do
      {
          // Etch in the direction indicated by the
          // arrow keys that the user enters
          key = Move();

          switch (key.Key)
          {
              case ConsoleKey.Z:
                  // Undo the previous Move
                  if (path.Count >= 1)
                  {
                      currentPosition = (Cell)path.Pop();
                      Console.SetCursorPosition(
                          currentPosition.X, currentPosition.Y);
                      Undo();
                  }
                  break;

              case ConsoleKey.DownArrow:
              case ConsoleKey.UpArrow:
              case ConsoleKey.LeftArrow:
              case ConsoleKey.RightArrow:
                  // SaveState()
                  currentPosition = new Cell(
                      Console.CursorLeft, Console.CursorTop);
                  path.Push(currentPosition);
                  break;

              default:
                  Console.Beep();  // Added in C# 2.0
                  break;
          }

      }
      while (key.Key != ConsoleKey.X);  // Use X to quit

  }
}

public struct Cell
{
    // Use read-only field prior to C# 6.0
    public int X { get; }
    public int Y { get; }
    public Cell(int x, int y)
    {
        X = x;
        Y = y;
    }
}