在处理流水号时，一般需要把对应的整数转换为相应位数的字符串。

        /// <summary>
        /// 把整数转换为指定位数的字符串
        /// </summary>
        /// <param name="slen">位数(这里允许最大32位)</param>
        /// <param name="maxSN">整数</param>
        /// <returns></returns>
        public string setSN(int slen, int maxSN)
        {
            string sn = "00000000000000000000000000000000";
            sn = sn.Substring(0, slen - (maxSN + 1).ToString().Length) + (maxSN + 1).ToString();
            if (maxSN.ToString().Length >= slen)
            {
                sn = maxSN.ToString();
            }
            return sn;
        }