C# 随机数类

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");
                }
            }