I'm simply trying to get a percentage.
irb(main):001:0> (25 / 50) * 100
=> 0
This should most definitely equal 50, as confirmed by my calculator (copied and pasted the same equation into gcalc). Why does Ruby refuse to do this?
+8
A:
It's doing integer division.
Basically, 25 is an integer (a whole number) and so is 50, so when you divide one by the other, it gives you another integer.
25 / 50 * 100 = 0.5 * 100 = 0 * 100 = 0
The better way to do it is to first multiply, then divide.
25 * 100 / 50 = 2500 / 50 = 50
You can also use floating point arithmetic explicitly by specifying a decimal point as in:
25.0 / 50.0 * 100 = 0.5 * 100 = 50
Matthew Scharley
2009-09-19 07:31:11
Thanks guys! I was calculating the percentage completed of opening a file in open-uri. Here's what I used: percent = (file_downloaded.to_f/file_length.to_f) * 100
c00lryguy
2009-09-19 07:41:55
Use the second form then. It's easier than trying to convert to floating point numbers.
Matthew Scharley
2009-09-19 08:02:10
Or rather, the first solution. The multiply then divide one. You know what I mean.
Matthew Scharley
2009-09-19 08:04:40
+2
A:
Because you're dividing an integer by an integer, so the result is getting truncated to integer (0.5 -> 0) before getting multiplied by 100.
But this works:
>> (25 / 50) * 100
=> 0
>> (25.0 / 50) * 100
=> 50.0
Daniel Pryden
2009-09-19 07:32:23