设计模式之工厂模式

 public class Operation
    {  
        private double _numberA = 0;
        private double _numberB = 0;

        public double NumberA { get; set; }
        public double NumberB { get; set; }

        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }

 //加发类
    public class OperationAdd : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }

    //减法类
    public class OperationSub : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA - NumberB;
            return result;
        }
    }

    //乘法类
    public class OperationMul : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA *NumberB;
            return result;
        }
    }

    //除法类
    public class OperationDiv: Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA / NumberB;
            return result;
        }
    }

  public  class OperationFactory
    {
        public static Operation createOperate(string operate)
        {
            Operation oper = null;
            switch (operate)
            {
                case "+":
                    oper=new OperationAdd();
                    break;
                case "-":
                    oper=new OperationSub();
                    break;
                case "*":
                    oper=new OperationMul();
                    break;
                case "/":
                    oper=new OperationDiv();
                    break;
            }
            return oper;
        }

    }

  static void Main(string[] args)
        {
            try
            {
                Console.Write("请输入数字A:");
                string strNumberA = Console.ReadLine();
                Console.Write("请选择运算符号（+，-，*，/）:");
                string strOperate = Console.ReadLine();
                Console.Write("请选择数字B:");
                string strNumberB = Console.ReadLine();
                Operation oper;
                oper = OperationFactory.createOperate(strOperate);
                oper.NumberA = Convert.ToDouble(strNumberA);
                oper.NumberB = Convert.ToDouble(strNumberB);
                double result = oper.GetResult();
                Console.WriteLine("结果是:" + result);
                Console.ReadLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine("您输入的有错:"+ex.Message);
            }
        }