static void Main(string[] args)        {            int length = args.Length;                        if (0 == length)            {                for (int i = 0; i < 20; i++)                {                    ShowTest(false);                }                Console.WriteLine("你一共答对" + m_correctNum + "道题，共20道题");            }            else if (2 == length)            {                if ("-c" == args[0])                {                    string str = args[1];                    if (IsPositiveInt(str))                    {                        int count = int.Parse(str);                        for (int i = 0; i < count; i++)                        {                            ShowTest(true);                        }                    }                    else                    {                        Console.WriteLine("题目数量必须是 正整数！");                    }                }            }

static private void ShowTest(bool showResult)        {            string expression = CreateExpression();  //生成试题            Queue<string> qexp = SplitExpress(expression); //把表达式存入队列            List<string> exp = InorderToPostorder(qexp); //表达式由中缀转为后缀            double result = 0;            IsResult(exp, out result);//根据后缀表达式计算结果            if (showResult)            {//打印试题及结果                Console.WriteLine(expression + "=                                 " + result);            }            else            {//出题,并读入用户输入的值,判断是否正确                Console.WriteLine(expression);                Console.Write("?");                string input = Console.ReadLine();                if (IsNumeric(input))                {                    double num = double.Parse(input);                    if (num == result)                    {                        Console.WriteLine("答对啦，你真是个天才！");                        m_correctNum++;                    }                    else                    {                        Console.WriteLine("再想想吧，答案似乎是" + result + "喔！");                    }                }            }                    }

static private string CreateExpression()        {            string expression = string.Empty;            int num;            int index;            char op;            List<int> position = new List<int>() {0, 2, 4 };            List<char> oplist = new List<char>() { ‘+‘,‘-‘, ‘*‘, ‘/‘};            List<string> divlist = new List<string>() { "1","2","4","5","8"};            List<string> expList = new List<string>();            num = ran.Next(10);            expList.Add(num.ToString());            for (int i = 0; i < 3; i++)            {                index = ran.Next(oplist.Count());                op = oplist[index];                if (‘/‘ == op)                {                    oplist.RemoveAt(3);                    index = ran.Next(divlist.Count());                    num = int.Parse(divlist[index]);                }                else                {                    num = ran.Next(10);                 }                expList.Add(op.ToString());                expList.Add(num.ToString());            }            int pos;            index = expList.IndexOf("/");            if (-1 == index)            {                pos = position[ran.Next(3)];            }            else            {                if (1 == index)                {                    position.RemoveAt(1);                }                else if (3 == index)                {                    position.RemoveAt(2);                }                pos = position[ran.Next(position.Count())];            }            expList.Insert(pos, "(");            expList.Insert(pos + 4, ")");            foreach (string str in expList)            {                expression += str;            }            return expression;        }