LSP2After.cs

public class Shape
{
    public virtual void PrintArea()
    {
    }
}
public class Rectangle : Shape
{
    public int Height { get; set; }
    public int Width { get; set; }
    
    public virtual void SetHeight(int height)
    {
        this.Height = height;
    }
    public virtual void SetWidth(int width)
    {
        this.Width = width;
    }
    public override void PrintArea()
    {
        Console.WriteLine(this.Height * this.Width);
    }
}

public class Square : Shape
{
    public int Edge { get; set; }
    
    public virtual void SetEdge(int edge)
    {
        this.Edge = edge;
    }

    public override void PrintArea()
    {
        Console.WriteLine(Math.Pow(this.Edge, 2));
    }
}

var rect = new Rectangle();
rect.SetHeight(10);
rect.SetWidth(5);
System.Console.WriteLine(rect.PrintArea()); // Kết quả là 50

var square = new Square();
rect.SetEdge(10);
System.Console.WriteLine(rect.PrintArea()); // Kết quả là 100