why does double return this value? C#

Question

double sth = 250 - 249.99;
Console.WriteLine(sth);

Why does this return sth like 0.009994507, instead of 0.01?

Answer 1

Floating point numbers (in this case doubles) cannot represent decimal values exactly. For more info, see this page here

If you need a more accurate representation, use decimal instead.

Answer 2

because when you print the double you print the all double value not just the first x after point digits.

you can use String.Format to print only the first 2 numbers.

        double sth = 250.00d - 249.99d;
        string sthString = String.Format("{0:0.00}", sth);
        Console.WriteLine(sthString);

Answer 3

There are a lot of decimals that have infinite binary representation. What you're experiencing is exactly this case.

For more on this topic see: http://www.exploringbinary.com/why-0-point-1-does-not-exist-in-floating-point/