发布时间:2017-09-22编辑:佚名阅读(2480)
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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