四则运算

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！");
                    }
                }
            }

　　判断控制台传入主函数参数个数情况的处理

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！");
                    }
                }
            }
            
        }

　　进行出题或者人打印试题

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;
        }

　　利用栈的应用，将中序转换为后序，再将后序输出。随机数是生成4个，符号也是4个，分别用0丶1丶2丶3表示，括号先设置为每两个数之间。

运行后的图片：