操作流程：

1. 新建Operation类

2. 新建OperationAdd类，并继承Operation类

3. 新建OperationSub类，并继承Operation类

4. 新建OperationMul类，并继承Operation类

5. 新建OperationDiv类，并继承Operation类

6. 新建创造实例的工厂类OperationFactory

7. Main方法操作根据传入的运算符创造相对应的操作类，并执行相对应的运算逻辑

1、新建Operation类

    public class Operation
    {
        public double numberA { get; set; }
        public double numberB { get; set; }
        public virtual double getResult()
        {
            return 0;
        }
    }

2. 新建OperationAdd类，并继承Operation类

    public class OperationAdd : Operation
    {
        //实现操作加法运算
        public override double getResult()
        {
            double result = 0;
            result = numberA + numberB;
            return result;
        }
    }

3. 新建OperationSub类，并继承Operation类

    public class OperationSub : Operation
    {
        //实现减法操作
        public override double getResult()
        {
            double result = 0;
            result = numberA - numberB;
            return result;
        }
    }

4. 新建OperationMul类，并继承Operation类

    public class OperationMul : Operation
    {
        //实现乘法操作
        public override double getResult()
        {
            double result = 0;
            result = numberA * numberB;
            return result;
        }
    }

5. 新建OperationDiv类，并继承Operation类

    public class OperationDiv : Operation
    {
        //实现除法操作
        public override double getResult()
        {
            double result = 0;
            if (numberB == 0)
                throw new Exception("除数不能为0");
            result = numberA / numberB;
            return result;
        }
    }

6. 新建创造实例的工厂类OperationFactory

    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;
                default:
                    break;
            }
            return oper;
        }
    }

7. Main方法操作根据传入的运算符创造相对应的操作类，并执行相对应的运算逻辑

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Operation oper = OperationFactory.CreateOperate("+");
                oper.numberA = 3;
                oper.numberB = 2;
                double result = oper.getResult();
                Console.WriteLine(result);
                Console.ReadLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                Console.ReadLine();
                throw;
            }
        }
    }