···
class Program
{
static void Main(string[] args)
{
RectangeClass rec = new RectangeClass(4, 5);
int mianji = rec.Mianji();
int zhouchang = rec.Zhouchang();

        Console.WriteLine("{0} \n{1}", mianji, zhouchang);
        rec.UpDate(5, 6);



        RoundClass rou = new RoundClass(8);
        double s1 = rou.GetRoundDate(1);
        double s2 = rou.GetRoundDate(2);
        Console.WriteLine("{0}\n{1}", s1, s2);

        Console.ReadKey();
    }
}

···
···
class RectangeClass
{
//長
private int length;
//寬
private int width;

    //構(gòu)造函數(shù)初始化 通過參數(shù)去改變

    public RectangeClass(int length1, int width1)
    {//實例化時必須傳參 
        length = length1;
        width = width1;

    }

    //矩形周長
    public int Zhouchang()
    {
        int num = 0;
        num = 2 * (length + width);
        return num;
    }
    //面積

    public int Mianji()
    {


        return length * width;

    }

    //改變矩形長寬的方法
    public void UpDate(int _length, int _width)
    {

        length = _length;
        width = _width;
    }
}

···

···
class RoundClass
{
private double r;

    public RoundClass(double R)
    {//構(gòu)造函數(shù)初始化
        r = R;
    }

    public double GetRoundDate(int num)
    {
        double RoundNum = 0;
        if (num == 1)
        {
            RoundNum = 2 * Math.PI * r;
        }
        else if (num == 2)
        {
            RoundNum = Math.PI * r * r;
        }
        else
        {
            RoundNum = 0;
        }


        return RoundNum;
    }
}

···