Math.Round()并没有四舍五入

Math.Round()

色即是空，空即是色。

C#中的Math.Round()并不是使用的"四舍五入"法。其实在VB、VBScript、C#、J#、T-SQL中Round函数都是采用Banker’s rounding（银行家算法），即：四舍六入五取偶。事实上这也是IEEE的规范，因此所有符合IEEE标准的语言都应该采用这样的算法。如：

Math.Round(0.4) //result:0
Math.Round(0.6) //result:1
Math.Round(0.5) //result:0
Math.Round(1.5) //result:2
Math.Round(2.5) //result:2
Math.Round(3.5) //result:4
Math.Round(4.5) //result:4
Math.Round(5.5) //result:6
Math.Round(6.5) //result:6
Math.Round(7.5) //result:8
Math.Round(8.5) //result:8
Math.Round(9.5) //result:10

中国式四舍五入

千呼万唤始出来,犹抱琵琶半遮面。

.NET 2.0 开始，Math.Round 方法提供了一个枚举选项 MidpointRounding.AwayFromZero 可以用来实现传统意义上的"四舍五入"。即： Math.Round(4.5, MidpointRounding.AwayFromZero) = 5。

Math.Round(0.4, MidpointRounding.AwayFromZero); // result:0
Math.Round(0.6, MidpointRounding.AwayFromZero); // result:1
Math.Round(0.5, MidpointRounding.AwayFromZero); // result:1
Math.Round(1.5, MidpointRounding.AwayFromZero); // result:2
Math.Round(2.5, MidpointRounding.AwayFromZero); // result:3
Math.Round(3.5, MidpointRounding.AwayFromZero); // result:4
Math.Round(4.5, MidpointRounding.AwayFromZero); // result:5

总结

原始归一。

如果用这个计算小数的话，就不灵了！！！
必须用第七个重载方法，decimal Round(decimal d, int decimals, MidpointRounding mode)，这样计算出来的小数才是真正的中国式四舍五入！！

Math.Round(526.925, 2)
526.92Math.Round(526.925, 2,MidpointRounding.AwayFromZero)
526.92Math.Round((decimal)526.925, 2)
526.92Math.Round((decimal)526.925, 2,MidpointRounding.AwayFromZero)
526.93

直接上干货，举个栗子！！

    #region RoundModepublic enum RoundMode{/// <summary>/// 四舍五入/// </summary>AwayFromZero,/// <summary>/// 设置为四舍六入五取偶/// </summary>ToEven,/// <summary>/// 按精度进位/// </summary>Carry,/// <summary>/// 按精度舍尾/// </summary>Truncation,}#endregion#region 将金额格式化/// <summary>/// 将金额格式化/// </summary>/// <param name="d"></param>/// <returns></returns>public static decimal FormatDecimal(this object d){var result = 0m;if (!d.IsNullOrEmptyOrWhiteSpace()){result = Convert.ToDecimal(d);result = Round(result, 2, RoundMode.AwayFromZero);}return result;}/// <summary>/// 十进制四舍五入/// </summary>public static decimal Round(decimal value, int decimals = 0, RoundMode mode = RoundMode.AwayFromZero){if (mode == RoundMode.AwayFromZero || mode == RoundMode.ToEven){MidpointRounding mpMode = MidpointRounding.AwayFromZero;if (mode == RoundMode.ToEven)mpMode = MidpointRounding.ToEven;return Math.Round(value, decimals, mpMode);}else{decimal scale = Convert.ToDecimal(Math.Pow(10, decimals));decimal newValue = value * scale;if (mode == RoundMode.Carry)newValue = Math.Ceiling(newValue);elsenewValue = Math.Truncate(newValue);return newValue / scale;}}#endregion