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Math.Round Method (Double)

Rounds a double-precision floating-point value to the nearest integral value.

Namespace:  System
Assemblies:   mscorlib (in mscorlib.dll)
  System.Runtime.Extensions (in System.Runtime.Extensions.dll)

'Declaration
Public Shared Function Round ( _
	a As Double _
) As Double

Parameters

a
Type: System.Double

A double-precision floating-point number to be rounded.

Return Value

Type: System.Double
The integer nearest a. If the fractional component of a is halfway between two integers, one of which is even and the other odd, then the even number is returned. Note that this method returns a Double instead of an integral type.

NoteNote

For examples and comprehensive usage information about this and other overloads of the Round method, see the Round reference page.

Notes to Callers

Because of the loss of precision that can result from representing decimal values as floating-point numbers or performing arithmetic operations on floating-point values, in some cases the Round(Double) method may not appear to round midpoint values to the nearest even integer. In the following example, because the floating-point value .1 has no finite binary representation, the first call to the Round(Double) method with a value of 11.5 returns 11 instead of 12.

Module Example
   Public Sub Main()
      Dim value As Double = 11.1
      For ctr As Integer = 0 To 5    
         value = RoundValueAndAdd(value)
      Next
      Console.WriteLine()

      value = 11.5
      RoundValueAndAdd(value)
   End Sub 

   Private Function RoundValueAndAdd(value As Double) As Double
      Console.WriteLine("{0} --> {1}", value, Math.Round(value))
      Return value + .1
   End Function    
End Module 
' The example displays the following output: 
'       11.1 --> 11 
'       11.2 --> 11 
'       11.3 --> 11 
'       11.4 --> 11 
'       11.5 --> 11 
'       11.6 --> 12 
'        
'       11.5 --> 12

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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