mathematics expression gives wrong answer in java application

Question

I created a simple program to calculate the volume of a sphere. But something wrong with the following code line

double volume=(4/3)*PI*radius*radius*radius;

producing the wrong answer.but if i change that to

double volume=PI*radius*radius*radius*4/3;

now it's giving the correct answer.

But both equations are perfectly alright according algebra. So why I get the wrong answer for the first equation?

A programming language is not math. There are many differences ("traps"). I recommend you read a book on the programming language (so Java in this case). — Bernd Elkemann, Feb 15 '14 at 14:54
you should use casting for integer division, or change one operator to double - `4.0 / 3` — catch23, Feb 15 '14 at 14:55

Smutje · Answer 1 · 2014-02-15T15:02:16.613

3

4/3 is interpreted as integer-division which means flooring - you have to explicitely state a floating-point division: (double) 4/3 or 4.0/3.

edited Feb 15 '14 at 15:02

answered Feb 15 '14 at 14:52

Smutje

1

No, integer division does not mean rounding, but flooring. (`int x = 8/3; // x = 2`) – qqilihq Feb 15 '14 at 15:00
1

Not "may be interpreted." "Is interpreted." – djechlin Feb 15 '14 at 15:01
Upvoted for further commentary help. – Smutje Feb 15 '14 at 15:02

score 2 · Answer 2 · answered Feb 15 '14 at 14:51

2

4/3 == 1. Integer division.

Try 4.0/3 for float, or divide by 3 at the end.

answered Feb 15 '14 at 14:51

djechlin

score 0 · Answer 3 · answered Feb 15 '14 at 14:57

0

It is because (4/3) is integer division and equals 1 by truncation. You should write:

double volume = (double) 4/3 *PI*radius*radius*radius;

or

double volume = 4.0/3 *PI*radius*radius*radius;

answered Feb 15 '14 at 14:57

4pie0

3 Answers3