/// <summary>
        /// 该方法用于生成指定位数的随机字符串
        /// </summary>
        /// <param name="VcodeNum">参数是随机数的位数</param>
        /// <returns>返回一个随机数字符串</returns>
        public static string RndNumStr(int VcodeNum)
        {
            string[] source = { "0", "1", "1", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z" };

            string checkCode = String.Empty;
            Random random = new Random();
            for (int i = 0; i < VcodeNum; i++)
            {
                checkCode += source[random.Next(0, source.Length)];

            }

            return checkCode;
        }