C#使用虚方法求一个圆的面积和周长

//定义一个父类的虚方法
public abstract class Person
{

  public abstract double GetArea();public abstract double GetPrimeter();

}
//继承虚方法父类的子类
public class Circle : Person
{
private double _r;
public double R
{

        get { return _r; }set { _r = value; }}public Circle(double r){this.R = r;}public override double GetArea(){return Math.PI * R * R;}public override double GetPrimeter(){return Math.PI * R * 2;}
}

//子类创建一个实例对象并传入一个构造函数对应的参数
Circle c = new Circle(5);
Console.WriteLine($"Circle Area{c.GetArea()},primeter{c.GetPrimeter()}");