关于#c##的问题，请各位专家解答！

初学C＃ 详细一点

using System;

namespace ConsoleApp1
{
    public class Circle
    {
        /// <summary>
        /// 半径
        /// </summary>
        public double R { get; set; }
        public static int nums { get; set; }
        public Circle(int R)
        {
            this.R = R;
            Circle.nums++;
        }
        public double Area()
        {
            return Math.PI * Math.Pow(R,2);
        }
    }
    class Program
    {

        static void Main(string[] args)
        {
            var circle = new Circle(5);
            Console.WriteLine("面积：" + circle.Area());
            Console.WriteLine("圆实例数：" + Circle.nums);

            circle = new Circle(6);
            Console.WriteLine("面积：" + circle.Area());
            Console.WriteLine("圆实例数：" + Circle.nums);

            Console.ReadKey();
        }

    }
}