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Math.Round Method (Double, Int32, MidpointRounding)

Rounds a double-precision floating-point value to a specified number of fractional digits. A parameter specifies how to round the value if it is midway between two numbers.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Shared Function Round ( _
	value As Double, _
	digits As Integer, _
	mode As MidpointRounding _
) As Double

Parameters

value
Type: System.Double

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

digits
Type: System.Int32

The number of fractional digits in the return value.

mode
Type: System.MidpointRounding

Specification for how to round value if it is midway between two other numbers.

Return Value

Type: System.Double
The number nearest to value that has a number of fractional digits equal to digits. If value has fewer fractional digits than digits, value is returned unchanged.

ExceptionCondition
ArgumentOutOfRangeException

digits is less than 0 or greater than 15.

ArgumentException

mode is not a valid value of System.MidpointRounding.

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, Int32, MidpointRounding) method may not appear to round midpoint values as specified by the mode parameter. This is illustrated in the following example, where 2.135 is rounded to 2.13 instead of 2.14. This occurs because internally the method multiplies value by 10digits, and the multiplication operation in this case suffers from a loss of precision.

Module Example
   Public Sub Main()
      Dim values() As Double = { 2.125, 2.135, 2.145, 3.125, 3.135, 3.145 }
      For Each value As Double In values
         Console.WriteLine("{0} --> {1}", value, 
                           Math.Round(value, 2, MidpointRounding.AwayFromZero))
      Next 
   End Sub 
End Module 
' The example displays the following output: 
'       2.125 --> 2.13 
'       2.135 --> 2.13 
'       2.145 --> 2.15 
'       3.125 --> 3.13 
'       3.135 --> 3.14 
'       3.145 --> 3.15

.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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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