C# 大写字母A~Z与数字的相互转换

/// <summary>
        /// 把A~Z转换成0~25
        /// </summary>
        /// <param name="A_Z">A~Z 大写</param>
        /// <returns></returns>
        private int Char2Number(string A_Z) 
        {

            byte[] array = new byte[1];
            array = System.Text.Encoding.ASCII.GetBytes(A_Z);
            return (short)(array[0])-65;
        }

        /// <summary>
        /// 把0~25转换成A~Z
        /// </summary>
        /// <param name="number">数字范围在闭区间[0,25]</param>
        /// <returns></returns>
        private string NumberToChar(int number)
        {
       
            if (0 <= number && 25 >= number)
            {
                int num = number + 65;
                System.Text.ASCIIEncoding asciiEncoding = new System.Text.ASCIIEncoding();
                byte[] btNumber = new byte[] { (byte)num };
                return asciiEncoding.GetString(btNumber);
            }
            return "数字不在转换范围内";
        }