float variable wrong answer

Question

Possible Duplicate:
Java: Calculations returning wrong answer?

Please explane why following program not giving correct output.

class Test
{
    public static void main(String aa[])
    {
        float a=16.15 f;
        float b =10.0f;

        float c =a-b;
        System.out.println(c);
    }
}

/****************/ Out Put:-6.1499996

http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html — Mysticial, Dec 06 '12 at 22:04
floating points calculations can't results in exact precision for .15. — kosa, Dec 06 '12 at 22:04
There should be some canonical standard answer for this type of questions, no day passes without a dozen of 'em :-( — fvu, Dec 06 '12 at 22:05
When using floats, add an error margin epsylon, and check for c < epsylon. — Martol1ni, Dec 06 '12 at 22:08

score 1 · Answer 1 · answered Dec 06 '12 at 22:06

1

The problem lies with floats themselves, rather than your code, as per http://en.wikipedia.org/wiki/IEEE_floating-point_standard

For this case, consider either using doubles or BigDecimals

answered Dec 06 '12 at 22:06

Ina

4,220
5
28
43

score 0 · Answer 2 · answered Dec 06 '12 at 22:04

0

That's a perfectly normal consequence of floats not being able to store decimal values exactly.

answered Dec 06 '12 at 22:04

Louis Wasserman

182,351
25
326
397

score 0 · Answer 3 · answered Dec 06 '12 at 22:05

0

Because floats, being base-2 cannot exactly represent 16.15 and therefore the result of the subtraction is not exactly -6.15.

answered Dec 06 '12 at 22:05

tjltjl

1,479
8
18

score -1 · Answer 4 · answered Dec 06 '12 at 22:04

-1

The type float does not have good enough precision to return -6.15. double may not be enough either, floating point computations always have some margin of error.

answered Dec 06 '12 at 22:04

Erik Ekman

2,031
12
13

It's a question of which base it is in – tjltjl Dec 06 '12 at 22:06

float variable wrong answer

4 Answers4