Rounding to 2 decimal places, without using banker's rounding

Question

.NET and Compact Framework by default use banker's rounding which means that the value: 1,165 will be rounded to: 1,16.

sql server as a opposite rounds it to 1,17 as for me it is the correct behaviour.

Has anyone come across rounding topic and have a workaround for a Compact Framework? (In .net there is an additional parameter which has an influence on the rounding behaviour)

What would you like 1.16499 to round to? Always up, so 1.160001 would be 1.17? — Joachim Isaksson, Aug 13 '13 at 10:08
Would like to have: 1.16. In sql server: select Round(1.16499, 2) returns that value. — John, Aug 13 '13 at 10:09
Just to explain this. 1.1649999 Would round to 1.6, and 1.65 would round to 1.7. Basic Math really, 1.5 = round up. — Philip Gullick, Aug 13 '13 at 10:18

Joachim Isaksson · Answer 1 · 2013-08-13T10:29:00.780

3

Math.Floor(double) seems to be supported, so;

private static double RoundToTwo(double value)
{
    return Math.Floor(100*value + .5)/100;
}

Console.WriteLine(RoundToTwo(1.165));
> 1.17

Console.WriteLine(RoundToTwo(1.16499));
> 1.16

edited Aug 13 '13 at 10:29

answered Aug 13 '13 at 10:23

Joachim Isaksson

176,943
25
281
294

score 2 · Accepted Answer · edited May 23 '17 at 12:23

Here is a method you can use instead of decimal.round:

public static decimal RoundHalfUp(this decimal d, int decimals)
{
if (decimals < 0)
{
    throw new ArgumentException("The decimals must be non-negative", 
        "decimals");
}

decimal multiplier = (decimal)Math.Pow(10, decimals);
decimal number = d * multiplier;

if (decimal.Truncate(number) < number)
{
    number += 0.5m;
}
return decimal.Round(number) / multiplier;
}

Taken from: Why does .NET use banker's rounding as default?

This question also asks why .Net uses bankers rounding. So I believe it will be a good read for you.

To answer why

This bankers algorithm means that results collected will be evenly spread of rounding up/down when the decimal == .5, so really it is just to even out data results.

Here's another link which describes this by Mr. Skeet

Look at these input values: For x = 0.002 I get rounded: 0.010 (xml rounds to 0.000) using the above function ... — John, Aug 29 '13 at 08:00

score 1 · Answer 3 · answered Aug 13 '13 at 10:25

1

Try

    double number = 1.165;
    string RoundedNumber = number.ToString("f3");

Where 3 is the scale

answered Aug 13 '13 at 10:25

Mohammad abumazen

1,286
1
11
24

Rounding to 2 decimal places, without using banker's rounding

3 Answers3