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# random number

tyhooke cologne
Greenhorn
Posts: 2
anyone know a slick way to create a random number between a negitive number and it's corosponding positive one?
i.e. gimme a random # between -5 and 5
thanks
-tyhooke

Henry Wong
author
Marshal
Posts: 21501
84

Henry

Jeff Bosch
Ranch Hand
Posts: 805
A more generic solution may be:

The output:

tyhooke cologne
Greenhorn
Posts: 2
these help. thank you both!
-Tyhooke

Jeff Bosch
Ranch Hand
Posts: 805
You're welcome!

Patrick Joseph
Greenhorn
Posts: 11

This gives you a random index (range of 0 to [array length - 1]) that will then give you the random contents (-5 to 5).
[ January 12, 2005: Message edited by: PJ Chin ]

Jeff Bosch
Ranch Hand
Posts: 805
Sure, but what happens when the user comes back and says, "Oh, now we need -10 to 10"? The hard-coded values method would need to be rewritten, where the general method would not. I always try to think "Reusability" when I write code, and part of that is not having any hard-coded values (except perhaps in the testing/driver program)...

David Harkness
Ranch Hand
Posts: 1646
Originally posted by Jeff Bosch:
int random = r.nextInt( 2 * number ) - number;
Keep in mind that Random.nextInt(number) returns a value in the range [0, number), meaning 0, 1 ... number - 1. It will not return number itself. Thus the general solution should be changed to

Jeff Bosch
Ranch Hand
Posts: 805
Ah, good point! I'd whipped that solution up in haste and something about it just didn't feel right, but I didn't really have time to go back to it.

Layne Lund
Ranch Hand
Posts: 3061
To add more flexibility, you may want to write a method with the following signature:

This would return a random integer between min and max. I'll leave the implementation as the proverbial exercise for the reader. However, it shouldn't be difficult to modify Jeff's program above for this purpose.

Layne