Rounding Error...Please help

[ywchan]

I have written the following codes:

double mean = 313.4;
int fieldValue = 321;
double result = ((double)fieldValue) - mean;
MessageBox.Show(result.ToString());
MessageBox.Show(Math.Pow(result,2).ToString());

However, for the value of result, I got 7.6000000000000227 instead of 7.6
This made my calculation wrong...

Any idea to solve it?

[Jon Skeet [C# MVP]]

ywchan <yw****@gmail.com> wrote:

I have written the following codes:

double mean = 313.4;
int fieldValue = 321;
double result = ((double)fieldValue) - mean;
MessageBox.Show(result.ToString());
MessageBox.Show(Math.Pow(result,2).ToString());

However, for the value of result, I got 7.6000000000000227 instead of 7.6
This made my calculation wrong...

Any idea to solve it?

See http://www.pobox.com/~skeet/csharp/floatingpoint.html

In short, the value stored as "mean" isn't 313.4 (which a double can't
represent) - it's

313.3999999999999772626324556767940521240234375

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Marko Becirevic]

> I have written the following codes:

double mean = 313.4;
int fieldValue = 321;
double result = ((double)fieldValue) - mean;
MessageBox.Show(result.ToString());
MessageBox.Show(Math.Pow(result,2).ToString());

However, for the value of result, I got 7.6000000000000227 instead of 7.6
This made my calculation wrong...

Any idea to solve it?

0.1 can't be binary written with final number of digits. 0.4 = 4 * 0.1, so
here is your 'error'.