随机生成8位数 大小写字母加数字

 byte[] r = new byte[8];
                int ran;
Random rand = new Random((int)(DateTime.Now.Ticks%1000000));
//生成8字节原始数据
for (int i = 0; i < 8; i++)
    //while循环剔除非字母和数字的随机数
    do
    {
        //数字范围是ASCII码中字母数字和一些符号
        ran = rand.Next(48, 122);
        r[i] = Convert.ToByte(ran);
    } while ((ran >= 58 && ran <= 64) || (ran >= 91 && ran <= 96));
//转换成8位String类型               
string randomID = Encoding.ASCII.GetString(r);