Why 0.3 - (3 * 0.10) = 5.4411512312578E-17?

Question

I'm really confused. My code:

        Console.WriteLine(myChanges + " TEN METHOD " +  (ten_num * TEN));(This for debug)
        if ((myChanges - (ten_num * TEN)) >= 0)
        {

        }else
            print error message

Like myChannges = 0.3 ; TEN = 0.1; ten_num = 3, but when I print (myChanges - (ten_num * TEN)) it equals 5.4411512312578E-17

Why not 0? Any solutions?

simple answer: you are giving decimal values that cannot be precisely represented as floating point (base 2) numbers. — Red Alert, Apr 25 '14 at 01:43

score 11 · Answer 1 · answered Apr 25 '14 at 01:42

11

This is due to the rounding errors inherent to floating point operations. See http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html for details.

answered Apr 25 '14 at 01:42

Tarik

10,206
1
20
37

score 1 · Answer 2 · answered Apr 25 '14 at 02:08

As has already been answered, floats/doubles have rounding errors. To get around this you could consider using BigDecimal objects or BigInteger objects. They are slower but much more accurate. Plus they can basically hold as many digits as you please.

Why 0.3 - (3 * 0.10) = 5.4411512312578E-17?

2 Answers2