自定义数字格式化（包括是否千分符显示，小数保留位数）

 

/// <summary>
        /// 格式化数字
        /// </summary>
        /// <param name="input">输入的数字</param>
        /// <param name="len">小数点保留位数(四舍五入)</param>
        /// <param name="bsep">是否千分符显示</param>
        /// <param name="separator">千分符号，默认为逗号(,)</param>
        /// <returns>格式化后的数字</returns>
        public static string FormatNumber(string input, int len, bool bsep, string separator)
        {
            string[] nums = input.Split('.');
            string num1 = "";
            string num2 = "";

            if (bsep && separator.Length == 0)
            {
                separator = ",";
            }

            if (bsep)
            {
                num1 = Regex.Replace(nums[0], @"(?<!-|^)(\d{3})", separator +"$1", RegexOptions.RightToLeft);
            }
            else
            {
                num1 = nums[0];
            }

            if (nums.Length == 2)
            {
                num2 = GetDecimal(nums[1], len);
            }

            if (num2.Length > 0)
            {
                if (len > 0)
                {
                    return num1 + "." + num2;
                }
                else if (Regex.IsMatch(num2,"[5-9]"))
                {
                    num1 = (Convert.ToInt32(nums[0]) + 1).ToString();
                    if (bsep)
                    {
                        num1 = Regex.Replace(num1, @"(?<!-|^)(\d{3})", separator + "$1", RegexOptions.RightToLeft);
                    }                   
                    

                    return num1;
                }

                return num1;
                
            }

            
            return num1;
        }

        /// <summary>
        /// 获得小数
        /// </summary>
        /// <param name="input">输入的小数</param>
        /// <param name="len">小数保留的位数</param>
        /// <returns>格式化后的小数</returns>
        public static string GetDecimal(string input, int len)
        {
            if (len < 0)
            {
                len = 0;
            }
            if (input.Length <= len)
            {
                return input.PadRight(len, '0');
            }

            if (len > 0 && Regex.IsMatch(input[len].ToString(), "[5-9]"))
            {
                return (Convert.ToInt32(input.Substring(0, len)) + 1).ToString().PadLeft(len,'0');
            }

            if (len == 0)
            {
                return input.Substring(0, 1);
            }

            return input.Substring(0, len);
           
        }