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Math.Round Method (Double, Int32, MidpointRounding)

Note: This method is new in the .NET Framework version 2.0.

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

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

public static double Round (
	double value,
	int digits,
	MidpointRounding mode
)
public static double Round (
	double value, 
	int digits, 
	MidpointRounding mode
)
public static function Round (
	value : double, 
	digits : int, 
	mode : MidpointRounding
) : double

Parameters

value

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

digits

The number of significant digits (precision) in the return value.

mode

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

Return Value

The number nearest value with a precision equal to digits. If value is halfway between two numbers, one of which is even and the other odd, then the mode parameter determines which number is returned. If the precision of value is less than digits, then value is returned unchanged.

Exception typeCondition

ArgumentOutOfRangeException

digits is less than 0 or greater than 15.

ArgumentException

mode is not a valid value of System.MidpointRounding.

The digits parameter specifies the number of significant digits in the return value and ranges from 0 to 15. If digits is zero, then a integer is returned.

The maximum total number of integral and fractional digits that can be returned is 15. If the rounded value contains more than 15 digits, the 15 most significant digits are returned. If the rounded value contains 15 or fewer digits, the integral digits and as many fractional digits as the digits parameter specifies are returned.

The behavior of this method follows IEEE Standard 754, section 4. The kind of rounding that is performed if mode is ToEven is sometimes called rounding to nearest, or banker's rounding.

The following code example demonstrates the Round method in conjunction with the MidpointRounding enumeration. Although the code example rounds decimal numbers, the Round method rounds double-precision floating-point numbers in a similar way.

// This example demonstrates the Math.Round() method in conjunction 
// with the MidpointRounding enumeration.
using System;

class Sample 
{
    public static void Main() 
    {
    decimal result = 0.0m;
    decimal posValue =  3.45m;
    decimal negValue = -3.45m;

// By default, round a positive and a negative value to the nearest even number. 
// The precision of the result is 1 decimal place.

    result = Math.Round(posValue, 1);
    Console.WriteLine("{0,4} = Math.Round({1,5}, 1)", result, posValue);
    result = Math.Round(negValue, 1);
    Console.WriteLine("{0,4} = Math.Round({1,5}, 1)", result, negValue);
    Console.WriteLine();

// Round a positive value to the nearest even number, then to the nearest number away from zero. 
// The precision of the result is 1 decimal place.

    result = Math.Round(posValue, 1, MidpointRounding.ToEven);
    Console.WriteLine("{0,4} = Math.Round({1,5}, 1, MidpointRounding.ToEven)", result, posValue);
    result = Math.Round(posValue, 1, MidpointRounding.AwayFromZero);
    Console.WriteLine("{0,4} = Math.Round({1,5}, 1, MidpointRounding.AwayFromZero)", result, posValue);
    Console.WriteLine();

// Round a negative value to the nearest even number, then to the nearest number away from zero. 
// The precision of the result is 1 decimal place.

    result = Math.Round(negValue, 1, MidpointRounding.ToEven);
    Console.WriteLine("{0,4} = Math.Round({1,5}, 1, MidpointRounding.ToEven)", result, negValue);
    result = Math.Round(negValue, 1, MidpointRounding.AwayFromZero);
    Console.WriteLine("{0,4} = Math.Round({1,5}, 1, MidpointRounding.AwayFromZero)", result, negValue);
    Console.WriteLine();
    }
}
/*
This code example produces the following results:

 3.4 = Math.Round( 3.45, 1)
-3.4 = Math.Round(-3.45, 1)

 3.4 = Math.Round( 3.45, 1, MidpointRounding.ToEven)
 3.5 = Math.Round( 3.45, 1, MidpointRounding.AwayFromZero)

-3.4 = Math.Round(-3.45, 1, MidpointRounding.ToEven)
-3.5 = Math.Round(-3.45, 1, MidpointRounding.AwayFromZero)

*/

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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