C# adding doubles ends with .000000001

Question

Why does this code produce the correct answer, except for the .000000001 at the end?

I have a DataGridView, that in a column has prices. This code goes down the grid, gets the values and adds them up.

double pp = 0;
for (int i = 0; i < PPUTDG.RowCount; i++)
{
    try
    {
      pp = pp + Convert.ToDouble(PPUTDG[16, i].Value.ToString().Replace("$",""));
    }
    catch { }
}

I then call .ToString() on pp. The values should add to 6240.75, except I get 6240.75000000001.

Thanks.

http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html — Bart Friederichs, Jul 09 '13 at 06:25
Read up on this topic here: http://stackoverflow.com/questions/618535/what-is-the-difference-between-decimal-float-and-double-in-c — Michael Bray, Jul 09 '13 at 06:29
I thought that since the numbers weren't overly large, a double would be fine. Guess not. Thanks! — Lift, Jul 09 '13 at 06:35

score 4 · Accepted Answer · answered Jul 09 '13 at 06:27

There is a lot to be found about this. I already gave one, this: http://floating-point-gui.de/basic/ is another.

In short:

"...internally, computers use a format (binary floating-point) that cannot accurately represent a number like 0.1, 0.2 or 0.3 at all."

Make sure you really need a floating point type. When dealing with money for example, it is better to use decimal or an integer and do your calculations in cents.

A good rule-of-thumb can be that it is OK to use a floating point type if the decimal-rounding errors are no problem in your application. Otherwise, use something else.

I like it when problems are so easily solved, thanks! I'll accept your answer when the time limits up. — Lift, Jul 09 '13 at 06:33

score 1 · Answer 2 · answered Jul 09 '13 at 06:33

1

For financial calculations use decimal type instead of double or float types.

answered Jul 09 '13 at 06:33

Eldar Agalarov

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C# adding doubles ends with .000000001

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