生成随机字母字符串(数字字母混和)

        /// 生成随机字母字符串(数字字母混和)
        /// 
        /// 待生成的位数
        /// 生成的字母字符串
        private string GenerateCheckCode(int codeCount)
        {
            int rep = 0;
            string str = string.Empty;
            long num2 = DateTime.Now.Ticks + rep;
            rep++;
            Random random = new Random(((int)(((ulong)num2) & 0xffffffffL)) | ((int)(num2 >> rep)));
            for (int i = 0; i < codeCount; i++)
            {
                char ch;
                int num = random.Next();
                if ((num % 2) == 0)
                {
                    ch = (char)(0x30 + ((ushort)(num % 10)));
                }
                else
                {
                    ch = (char)(0x41 + ((ushort)(num % 0x1a)));
                }
                str = str + ch.ToString();
            }
            return str;
        }