class Calculator01
    {
        public double Num1 { get; set; }
        public double Num2 { get; set; }

        public double Run(string operate)
        {
            switch(operate)
            {
                case "+":
                    return Num1 + Num2;
                case "-":
                    return Num1 - Num2;
                case "*":
                    return Num1 * Num2;
                case "/":
                    if (Num2 == 0)
                    {
                        throw new Exception("除数不能为0");
                    }

                    return Num1 / Num2;
                default:
                    throw new Exception("未知的操作符");
            }
        }
    }

    class Calculator02
    {
        // 内置委托Action、Func、Predicate的区别：
        // Action可以有多个参数但不可有返回值；
        // Func可以有多个参数且最后一个参数固定是返回值；
        // Predicate只能有1个参数且返回布尔值。  
        private Dictionary<string, Func<double, double, double>> map = new Dictionary<string, Func<double, double, double>>();

        public double Num1 { get; set; }
        public double Num2 { get; set; }        

        public Calculator02()
        {          
            // 注册操作符到方法的映射
            map.Add("+", Add);
            map.Add("-", Sub);
            map.Add("*", Mul);
            map.Add("/", Div);
        }

        public double Run(string operate)
        {
            if (!map.ContainsKey(operate))
                throw new Exception("未知的操作符");

            return map[operate](Num1, Num2);
        }

        private double Add(double num1, double num2)
        {
            return Num1 + Num2;
        }

        private double Sub(double num1, double num2)
        {
            return Num1 - Num2;
        }

        private double Mul(double num1, double num2)
        {
            return Num1 * Num2;
        }

        private double Div(double num1, double num2)
        {
            if (Num2 == 0)
            {
                throw new Exception("除数不能为0");
            }

            return Num1 / Num2;
        }
    }