随机数类        Random            

    Random ran = new Random();//初始化            

    double a = ran.Next(10);            

    int b = ran.Next(s.Length);          

    Console.WriteLine(a);

练习

            随机出验证码，对照输入，判断是否正确

string s = "abcdefghijklmnopqrstuvwxyzABCDEFGHJKLMNOPQRSTUVWXYZ0123456789";            Random ran = new Random();            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！");            }            else            {                Console.WriteLine("输入错误！");            }            Console.ReadLine();            Console.Clear();            Console.WriteLine("123");

 

           输入验证码

string s = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";            Random ran = new Random();            for (; ; )            {                string a = "";                for (int i = 1; i <= 4; i++)                {                    a += s.Substring(ran.Next(s.Length), 1);                }                Console.WriteLine(a);                Console.WriteLine("请输入验证码：");                string b = Console.ReadLine();                if (b.ToLower() == a.ToLower())                {                    Console.WriteLine("输入正确");                    break;                }                else                {                    Console.Clear();                    Console.WriteLine("输入错误");                }            }