面向对象下计算器的编码实现

1、封装

首先是新建一个运算类（Calcultor.cs），它包含两个属性strNumA和strNumB，用以储存计算时的两个数，此外，还有一个虚方法Getresult()，用以得到运算的结果。

    public class calculator
    {
        /// <summary>
        /// 定义运算类的属性
        /// </summary>
        private double dblNumA = 0,dblNumB=0;

        /// <summary>
        /// 定义属性dblNumA的操作方法
        /// </summary>
        public double dblnuma
        {
            get { return dblNumA; }
            set { dblNumA = value; }
        }

        /// <summary>
        /// 定义属性dblNumB的操作方法
        /// </summary>
        public double dblnumb
        {
            get { return dblNumB; }
            set { dblNumB = value; }
        }

        /// <summary>
        /// 得到运算结果
        /// </summary>
        /// <returns>dblresult</returns>
        public virtual string GetResult()
        {
            string dblResult ="0";
            return dblResult;
        }
    }

2、继承

然后将操作加、减、乘、除写成运算类的子类，继承运算类后重写Getresult()。

    /// <summary>
    /// 加法类
    /// </summary>
    class OperationAdd : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            dblresult = (dblnuma + dblnumb).ToString();
            return dblresult;
        }
    }
    /// <summary>
    /// 减法类
    /// </summary>
    class OperationSub : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            dblresult = (dblnuma - dblnumb).ToString();
            return dblresult;
        }
    }
    /// <summary>
    /// 乘法类
    /// </summary>
    class OperationMul : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            dblresult = (dblnuma * dblnumb).ToString();
            return dblresult;
        }
    }
    /// <summary>
    /// 除法类
    /// </summary>
    class OperationDiv : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            if (dblnumb != 0)
            {                
                dblresult = (dblnuma / dblnumb).ToString();
            }
            else
            {
                dblresult = "除数不能为0！";
            }
            return dblresult;
        }
    }

3、多态

再用一个单独的类创造实例的过程。

    public class factory
    {
        public static calculator createOperation(string strOperation)
        {
            calculator cal = null;
            switch (strOperation)
            {
                case "+":
                {
                    cal = new OperationAdd();
                    break;
                }
                case "-":
                {
                    cal = new OperationSub();
                    break;
                }
                case "*":
                {
                    cal = new OperationMul();
                    break;
                }
                case "/":
                {
                    cal = new OperationDiv();
                    break;
                }
            }
            return cal;
        }
    }