public class DecimalHelper

    {

        /// <summary>

        /// Decimal类型截取保留N位小数并且不进行四舍五入操作

        /// </summary>

        /// <param name="d"></param>

        /// <param name="n"></param>

        /// <returns></returns>

        public static decimal CutDecimalWithN(decimal d, int n)

        {

            string strDecimal = d.ToString();

            int index = strDecimal.IndexOf(".");

            if (index == -1 || strDecimal.Length < index + n + 1)

            {

                strDecimal = string.Format("{0:F" + n + "}", d);

            }

            else

            {

                int length = index;

                if (n != 0)

                {

                    length = index + n + 1;

                }

                strDecimal = strDecimal.Substring(0, length);

            }

            return Decimal.Parse(strDecimal);

        }

        /// <summary>

        ///  Decimal类型截取保留N位小数向上取

        /// </summary>

        /// <param name="d"></param>

        /// <param name="n"></param>

        /// <returns></returns>

        public static decimal Ceiling(decimal d, int n)

        {

            decimal t = decimal.Parse(Math.Pow(10, n).ToString());

            d = Math.Ceiling(t * d);

            return d / t;

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            Console.WriteLine();

            decimal Dec = 12.12345M;

            for (int i = 0; i < 10; i++)

            {

                Console.WriteLine($"{Dec} 保留{i} 位小数不进行四舍五入操作：" + DecimalHelper.CutDecimalWithN(Dec, i));

            }

            Console.WriteLine();

            for (int i = 0; i < 10; i++)

            {

                Console.WriteLine($"{Dec} 保留{i} 位小数向上取整操作：" + DecimalHelper.Ceiling(Dec, i));

            }

            Console.Read();

        }

    }