int number, i;
        StringBuilder myStr = new StringBuilder(string.Empty);

        //随机数种子
        Random random = new Random();

//数字和大小写字母
                for (i = 0; i < codeLength; i++)
                {
                    //随机的整数
                    number = random.Next();

                    //字符从0-9、A-Z、a-z中随机产生，一共62个字符，对应的ASCII码是48-57、65-90、97-122
                    //%是取余，n%62的余数范围是0-61
                    //0-9(48-57)有10个字符，对应余数0-9：余数 + 48
                    //A-Z(65-90)是26个字符，对应余数10-35：余数 + 65 - 10 = 余数 + 55
                    //a-z(97-122)是26个字符，对应余数36-61：余数 + 97 - 36 = 余数 + 61
                    number = number % 62;
                    if (number < 10)
                    {
                        number += 48;
                    }
                    else if (number < 36)
                    {
                        number += 55;
                    }
                    else
                    {
                        number += 61;
                    }
                    //累加检验码字符串
                    myStr.Append((char)number).ToString();
                }