public abstract class Calculator    {        public double Number1 { get; set; }        public double Number2 { get; set; }        public abstract double Calculate();    }

class Add : Calculator    {        public Add(double n1,double n2)        {            this.Number1 = n1;            this.Number2 = n2;        }        public override double Calculate()        {            return Number1 + Number2;        }    }

class Sub : Calculator    {        public Sub(double n1,double n2 )        {            this.Number1 = n1;            this.Number2 = n2;        }        public override double Calculate()        {            return Number1 - Number2;        }    }

 

class Program    {        static void Main(string[] args)        {            Console.WriteLine("第一个数");            double Number1 = Convert.ToDouble(Console.ReadLine());            Console.WriteLine("操作符");            string  Operate= Console.ReadLine();            Console.WriteLine("第二个数");            double Number2= Convert.ToDouble(Console.ReadLine());            Calculator calculator = null;            switch (Operate)            {                case "+":                    calculator = new Add(Number1, Number2);                     break;                case "-":                    calculator = new Sub(Number1, Number2);                    break;            }            if (calculator!=null)            {                Console.WriteLine("结果是：{0}",calculator.Calculate());            }            else            {                Console.WriteLine("没有这种操作");            }        }    }

优化：

 Calculator calculator = GetComputeObject(Operate, Number1, Number2);

private static Calculator GetComputeObject(string perate, double number1, double number2)        {            Calculator result = null;            switch (perate)            {                case "+":                    result = new Add(number1, number2);                    break;                case "-":                    result = new Sub(number1, number2);                    break;            }            return result;        }