Problems with Math.Round

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  • Start date Start date
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Guest

Hello everyone

I have a problem with Math.Round, it´s ocurring some strange:

Math.Round(12.985) = 12.98, it´s wrong. It should be: 12.99

Why?? What is the problem?

Help ME !!!!

Renato
 
This is well treated in the docs. The default is "ToEven" rounding (AKA
Bankers rounding). This tries to prevent rounding errors by always rounding
in one direction. If the digit is mid-point, and the prior digit is an even
number, it rounds to even. If the number is odd, then rounds other way. The
kind of rounding you may have learned in school is always round up to next
digit - or away from zero.

decimal d1 = (decimal)12.985;
decimal d2 = Math.Round(d1, 2, MidpointRounding.ToEven);

decimal d3 = Math.Round(d1, 2, MidpointRounding.AwayFromZero);

decimal d4 = Math.Round((decimal)12.975, 2, MidpointRounding.ToEven);

Console.WriteLine("Value:{0} ToEven:{1} AwayFromZero:{2}
d4:{3}",d1,d2,d3,d4);
// Value:12.985 ToEven:12.98 AwayFromZero:12.99 d4-ToEven:12.98


--
William Stacey [C# MVP]
PowerLocker, PowerPad
www.powerlocker.com




| Hello everyone
|
| I have a problem with Math.Round, it´s ocurring some strange:
|
| Math.Round(12.985) = 12.98, it´s wrong. It should be: 12.99
|
| Why?? What is the problem?
|
| Help ME !!!!
|
| Renato
 
Please note, this is new to .NET 2.0.

In .NET 1.1, you need to role your own Round method like in this class:

public sealed class Math {

/// <summary>
/// Rounds the double value to round to a specified number of decimals.
Does not use Bankers Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <param name="digits">The number of digits to round to</param>
/// <returns>The rounded value</returns>
public static double Round(double value, int digits) {
return System.Math.Round(value +
(System.Math.Sign(value)/System.Math.Pow(10, digits+1)), digits);
}

/// <summary>
/// Rounds the double value to round to 0 decimals. Does not use Bankers
Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <returns>The rounded value</returns>
public static double Round(double value) {
return Round(value, 0);
}

/// <summary>
/// Rounds the decimal value to round to a specified number of decimals.
Does not use Bankers Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <param name="digits">The number of digits to round to</param>
/// <returns>The rounded value</returns>
public static decimal Round(decimal value, int digits) {
return System.Math.Round(value + Convert.ToDecimal(
System.Math.Sign(value)/System.Math.Pow(10, digits+1)), digits);
}

/// <summary>
/// Rounds the decimal value to round to 0 decimals. Does not use Bankers
Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <returns>The rounded value</returns>
public static decimal Round(decimal value) {
return Round(value, 0);
}

}


William Stacey said:
This is well treated in the docs. The default is "ToEven" rounding (AKA
Bankers rounding). This tries to prevent rounding errors by always
rounding
in one direction. If the digit is mid-point, and the prior digit is an
even
number, it rounds to even. If the number is odd, then rounds other way.
The
kind of rounding you may have learned in school is always round up to next
digit - or away from zero.

decimal d1 = (decimal)12.985;
decimal d2 = Math.Round(d1, 2, MidpointRounding.ToEven);

decimal d3 = Math.Round(d1, 2, MidpointRounding.AwayFromZero);

decimal d4 = Math.Round((decimal)12.975, 2, MidpointRounding.ToEven);

Console.WriteLine("Value:{0} ToEven:{1} AwayFromZero:{2}
d4:{3}",d1,d2,d3,d4);
// Value:12.985 ToEven:12.98 AwayFromZero:12.99 d4-ToEven:12.98


--
William Stacey [C# MVP]
PowerLocker, PowerPad
www.powerlocker.com




| Hello everyone
|
| I have a problem with Math.Round, it´s ocurring some strange:
|
| Math.Round(12.985) = 12.98, it´s wrong. It should be: 12.99
|
| Why?? What is the problem?
|
| Help ME !!!!
|
| Renato
Click to expand...
 
Thanks William

You have right !! But I'm working .NET 1.1, is this the problem.
 
Thanks Benny

I´m working .NET 1.1, your functions are OK.

Renato

Benny Skjold Tordrup said:
Please note, this is new to .NET 2.0.

In .NET 1.1, you need to role your own Round method like in this class:

public sealed class Math {

/// <summary>
/// Rounds the double value to round to a specified number of decimals.
Does not use Bankers Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <param name="digits">The number of digits to round to</param>
/// <returns>The rounded value</returns>
public static double Round(double value, int digits) {
return System.Math.Round(value +
(System.Math.Sign(value)/System.Math.Pow(10, digits+1)), digits);
}

/// <summary>
/// Rounds the double value to round to 0 decimals. Does not use Bankers
Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <returns>The rounded value</returns>
public static double Round(double value) {
return Round(value, 0);
}

/// <summary>
/// Rounds the decimal value to round to a specified number of decimals.
Does not use Bankers Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <param name="digits">The number of digits to round to</param>
/// <returns>The rounded value</returns>
public static decimal Round(decimal value, int digits) {
return System.Math.Round(value + Convert.ToDecimal(
System.Math.Sign(value)/System.Math.Pow(10, digits+1)), digits);
}

/// <summary>
/// Rounds the decimal value to round to 0 decimals. Does not use Bankers
Rounding.
/// </summary>
/// <param name="value">The value to round</param>
/// <returns>The rounded value</returns>
public static decimal Round(decimal value) {
return Round(value, 0);
}

}


William Stacey said:
This is well treated in the docs. The default is "ToEven" rounding (AKA
Bankers rounding). This tries to prevent rounding errors by always
rounding
in one direction. If the digit is mid-point, and the prior digit is an
even
number, it rounds to even. If the number is odd, then rounds other way.
The
kind of rounding you may have learned in school is always round up to next
digit - or away from zero.

decimal d1 = (decimal)12.985;
decimal d2 = Math.Round(d1, 2, MidpointRounding.ToEven);

decimal d3 = Math.Round(d1, 2, MidpointRounding.AwayFromZero);

decimal d4 = Math.Round((decimal)12.975, 2, MidpointRounding.ToEven);

Console.WriteLine("Value:{0} ToEven:{1} AwayFromZero:{2}
d4:{3}",d1,d2,d3,d4);
// Value:12.985 ToEven:12.98 AwayFromZero:12.99 d4-ToEven:12.98


--
William Stacey [C# MVP]
PowerLocker, PowerPad
www.powerlocker.com




| Hello everyone
|
| I have a problem with Math.Round, it´s ocurring some strange:
|
| Math.Round(12.985) = 12.98, it´s wrong. It should be: 12.99
|
| Why?? What is the problem?
|
| Help ME !!!!
|
| Renato
Click to expand...
Click to expand...
 
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