验证码

“验证码：xxxx”
“请输入验证码：”
“输入的位数不正确！”
大小写都行
“验证成功！/ 验证失败！”

          string a = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890";
            while (true) {
                Random b = new Random();
                string y = "";
                for (int x = 1; x < 5; x++)
                {

                    int c = b.Next(0, a.Length);
                    string d = a.Substring(c, 1);
                    y += d;

                }
                Console.WriteLine(y);
                string input = Console.ReadLine();
                input = input.ToLower();
                y = y.ToLower();
                if (input == y)
                {

                    Console.WriteLine("验证成功");
                    break;
                }
                else if (input.Length != y.Length)
                {
                    Console.WriteLine("输入的位数不正确，请重新输入：");
                }
                else 
                {
                    Console.WriteLine("验证失败,请重新输入：");
                }
            }            
           Console.Read();