Dividing long by long returns 0

Question

I am trying to calculate % of used diskspace in Windows and totaldrive denotes total diskspace of c drive in Long and freedrive dentoes free space in Long.

 long totaloccupied = totaldrive - freedrive;

Here calculating % of usage

 Long Percentageused =(totaloccupied/totaldrive*100);
 System.out.println(Percentageused);

The print statement returns 0. Can someone help as I am not getting the desired value

Heh. It was a long day that I enjoyed a float down the river... — cabbagery, Aug 08 '13 at 02:40
Why are you using `Long` instead of `long`? Also, please look at Java naming conventions for `percentageUsed`. — wchargin, Aug 08 '13 at 02:53

score 67 · Accepted Answer · answered Aug 08 '13 at 02:39

You are probably dividing a long with a long, which refers to (long/long = long) operation, giving a long result (in your case 0).

You can achieve the same thing by casting either operand of the division to a float type.

Long Percentageused = (long)((float)totaloccupied/totaldrive*100);

score 7 · Answer 2 · answered Aug 08 '13 at 02:38

7

You are doing integer division! Since totaloccupied is smaller than totaldrive, the division of both gives the answer 0. You should convert to double first:

double percentageUsed = 100.0 * totalOccupied / totalDrive;

Note that adding the decimal point to the 100 ensures it is treated as a double.

answered Aug 08 '13 at 02:38

gdiazc

2,108
4
19
30

1

if totalOccupied and totalDrive both are long, then even multiplying by 100.0 will result in 0.0 – Chintan Soni Jul 08 '16 at 06:40

score 1 · Answer 3 · answered Aug 08 '13 at 02:37

1

That will be evaluated left to right, the first integer division will return 0 (e.g. 8/10 evaluates to 0). Either convert values to floats or do 100*a/b. Floats will give you a more precise result.

answered Aug 08 '13 at 02:37

Jason C

38,729
14
126
182

`float` will *not* give a more precise result if the numbers involved are large. – paddy Aug 08 '13 at 02:41
It will if you do (float)(100*a)/(float)b. The two sides will differ by a relatively small order of magnitude, which is where most precision loss occurs. – Jason C Aug 08 '13 at 02:46
1

BTW, whoever came through and down voted every answer here, please leave a constructive comment. – Jason C Aug 08 '13 at 02:47
2

If the objective is an integer percentage, the 100*a/b solution, with a and b both long, would work well. Float or double is only needed to get answers like "85.5%". – Patricia Shanahan Aug 08 '13 at 02:49

Dividing long by long returns 0

3 Answers3

Linked

Related