Random:

Random ran=new Random();//初始化

int a=ran.Next(10);

Console.WhiteLine(a);

Console.ReadLine();

//随机出验证码，对照输入，判断是否正确；                        string s = "abcdefghijklmnopqistuvwxyzABCDEFGHIJKLMNOPQISTUVWXYZ0123456789";            Random ran = new Random();            for (; ; )            {                string biao = "";                for (int i = 1; i <= 4; i++)                {                    biao += s.Substring(ran.Next(s.Length), 1);                }                Console.WriteLine(biao);                Console.Write("请输入验证码：");                string shu = Console.ReadLine();                if (shu.ToLower() == biao.ToLower())                {                    Console.WriteLine("输入正确");                    break;                }                else                {                    Console.Clear();                    Console.WriteLine("输入错误！");                }            }            Console.ReadLine();