C#中Math.Round()實現中國式四舍五入

C#中Math.Round()實現中國式四舍五入

 

C#中的Math.Round()並不是使用的"四舍五入"法。其實在VB、VBScript、C#、J#、T-SQL中Round函數都是采用Banker's rounding（銀行家算法），即：四舍六入五取偶。事實上這也是IEEE的規范，因此所有符合IEEE標准的語言都應該采用這樣的算法。

.NET 2.0 開始，Math.Round 方法提供了一個枚舉選項 MidpointRounding.AwayFromZero 可以用來實現傳統意義上的"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重載后對比：   

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

   

   

但是悲劇的是，如果用這個計算小數的話，就不靈了！！！

必須用第七個重載方法，
decimal Round(decimal d, int decimals, MidpointRounding mode)

這樣計算出來的小數才是真正的中國式四舍五入！！

    

?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