设计的一个计算器类的源代码,很简陋哦,请各位高手不要见笑!

答案：  
//名字空间MyCalClass
//类名: CalClass
//无参的构造函数CalClass()
//6个用到的私有变量
//void PointClick()  按小数点
//string CE()  是计算器复位用的,clear函数
//string BackSpace(string Txt)  倒退键,参数是计算过程中现在显示的计算结果
//string NumClick(string Txt,int NumKey)  0-9数字键按下的响应,Txt是计算的当前结果,NumKey是按下的数字值
//string OpClick(string Txt,int OpKey) +,-,*,/,=几个键按下时的处理,Txt是计算的当前结果,OpKey是按下操作键的数字ID
namespace MyCalClass
{
    public class CalClass
    {
        private string ResultTxt;    //Get and Show The Result of the TextBox in application
        private bool PointIsDown;    //If the radix point was clicked;
        private double MidResult;    //To Store middle results
        private double Results;    //To store finally result
        private int LastClick;    //To sign last clicking button class,is number(1) or operator(2)
        private int LastOperator;    //To sign last clicked button of operator is who?0 is Null,1 is +,2 is - ,3 is *,4 is /,5 is =; 

       public CalClass()
        {
            ResultTxt = "0.";
            PointIsDown = false;
            MidResult = 0;
            Results = 0;
            LastClick = 0;
            LastOperator = 0;
        }
        public void PointClick()   //按下小数点后的函数处理
        {

            PointIsDown = true;
            return;
        }
        public string CE()  //按下CE键,清理计算器
        {
            ResultTxt = "0.";
            MidResult = 0;
            Results = 0;
            PointIsDown = false;
            LastClick = 0;
            LastOperator = 0;
            return ResultTxt;
        }
        public string BackSpace(string Txt)     //后退键按下后的处理函数
        {
            if(LastClick == 2)return Txt;      //如果上次的按键是操作,不是数字,直接返回,不能再退回
            if (Txt[Txt.Length - 1] == '.')       //计算器文本里最后一位是小数点时的情况:
            {
                if (PointIsDown == true) { PointIsDown = false; return Txt; }    //如果小数点按下了,则退去小数点
                else
                {
                    if (Txt.Length == 2 && Txt[0] != '0') return "0.";    //如果现在只有一位整数,"X."的情况,直接返回"0."
                    if (Txt.Length > 2) { ResultTxt = Txt.Remove(Txt.Length - 2, 2) + "."; return ResultTxt; }//否则,把最后一位去掉;
                }
            }
            else//如果最后一们不是小数点,很简单,直接把最后一们去掉就行了!
            {
                ResultTxt = Txt.Remove(Txt.Length - 1, 1);
                return ResultTxt;
            }
            return ResultTxt;//最后还要返回一个东西,程序里要求的,虽然根本运行不到这里!
        }
        public string NumClick(string Txt, int NumKey)//按下数字键(0-9)后的处理函数
        {
            //ResultTxt=Txt;
            LastClick = 1;//先标志一下,最后一次按键是"数字键"
            if (Txt[Txt.Length - 1] == '.')//最后一位是小数点的情况:
            {
                if (PointIsDown == true)//小数点已经被按下
                {
                    ResultTxt = Txt + NumKey.ToString();//直接把按下的数字加到计算结果字符串上
                }
                else//小数点没被按下的话
                {
                    if (Txt.Length == 2 && Txt[0] == '0')//如果现在的数值是0.的话,则把现在的数值直接变成按下的数字
                    {
                        ResultTxt = Txt.Replace("0", NumKey.ToString());
                    }
                    else
                    {
        &nbs

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