C#中Math.Round()实现中国式四舍五入

发布时间:2017-09-22 09:53:04编辑:佚名阅读(689)

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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。

总结的口诀是:四舍六入五考虑,五后非零就进一,五后皆零看奇偶,五前为偶应舍去,五前为奇要进一!

.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。

Round(Decimal)
Round(Double)
Round(Decimal, Int32)
Round(Decimal, MidpointRounding)
Round(Double, Int32)
Round(Double, MidpointRounding)
Round(Decimal, Int32, MidpointRounding)
Round(Double, Int32, MidpointRounding)

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

使用MidpointRounding.AwayFromZero重载后对比:   

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
Math.Round(5.5, MidpointRounding.AwayFromZero); // result:6
Math.Round(6.5, MidpointRounding.AwayFromZero); // result:7
Math.Round(7.5, MidpointRounding.AwayFromZero); // result:8
Math.Round(8.5, MidpointRounding.AwayFromZero); // result:9
Math.Round(9.5, MidpointRounding.AwayFromZero); // result:10

但是悲剧的是,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)
526.92
Math.Round(526.925, 2,MidpointRounding.AwayFromZero)
526.92
Math.Round((decimal)526.925, 2)
526.92
Math.Round((decimal)526.925, 2,MidpointRounding.AwayFromZero)
526.93

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  关键字:C#MathRound()四舍五入


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