用c#定义一个矩形类，进行长度和面积的计算（简化，使长宽只输入一次，周长和面积同时出来）

  class graph {
        double chang;
        double kuan;
        public double Chang { get => chang; set => chang = value; }
        public double Kuan { get => kuan; set => kuan = value; }

        public double GetCO()
        {
            return (this.Chang + this.Kuan) * 2;
        }
        public double GetSO()
        {
            return this.Chang * this.Kuan;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            graph c = new graph();
            Console.WriteLine("请输入长的值:");
            c.Chang = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("请输入宽的值:");
            c.Kuan = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("周长为：{0}",c.GetCO());
            Console.ReadKey();

            graph s = new graph();
            Console.WriteLine("请输入长的值:");
            s.Chang = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("请输入宽的值:");
            s.Kuan = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("面积为：{0}", s.GetSO());
            Console.ReadKey();
        }
    }