面向對象下計算器的編碼實現

1、封裝

首先是新建一個運算類（Calcultor.cs），它包含兩個屬性strNumA和strNumB，用以儲存計算時的兩個數，此外，還有一個虛方法Getresult()，用以得到運算的結果。

    public class calculator
    {
        /// <summary>
        /// 定義運算類的屬性
        /// </summary>
        private double dblNumA = 0,dblNumB=0;

        /// <summary>
        /// 定義屬性dblNumA的操作方法
        /// </summary>
        public double dblnuma
        {
            get { return dblNumA; }
            set { dblNumA = value; }
        }

        /// <summary>
        /// 定義屬性dblNumB的操作方法
        /// </summary>
        public double dblnumb
        {
            get { return dblNumB; }
            set { dblNumB = value; }
        }

        /// <summary>
        /// 得到運算結果
        /// </summary>
        /// <returns>dblresult</returns>
        public virtual string GetResult()
        {
            string dblResult ="0";
            return dblResult;
        }
    }

2、繼承

然後將操作加、減、乘、除寫成運算類的子類，繼承運算類後重寫Getresult()。

    /// <summary>
    /// 加法類
    /// </summary>
    class OperationAdd : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            dblresult = (dblnuma + dblnumb).ToString();
            return dblresult;
        }
    }
    /// <summary>
    /// 減法類
    /// </summary>
    class OperationSub : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            dblresult = (dblnuma - dblnumb).ToString();
            return dblresult;
        }
    }
    /// <summary>
    /// 乘法類
    /// </summary>
    class OperationMul : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            dblresult = (dblnuma * dblnumb).ToString();
            return dblresult;
        }
    }
    /// <summary>
    /// 除法類
    /// </summary>
    class OperationDiv : calculator
    {
        public override string GetResult()
        {
            string dblresult = "0";
            if (dblnumb != 0)
            {                
                dblresult = (dblnuma / dblnumb).ToString();
            }
            else
            {
                dblresult = "除數不能爲0！";
            }
            return dblresult;
        }
    }

3、多態

再用一個單獨的類創造實例的過程。

    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;
        }
    }