A Web-based News Reader
| Subject | Re: random number within a specified range? | ||||||||||||
| From | Don <nospam@nospam.com.au> | ||||||||||||
| Date | Thu, 09 Oct 2008 15:33:49 +0200 | ||||||||||||
| Newsgroups | digitalmars.D.learn | ||||||||||||
Jarrett Billingsley wrote: > On Sun, Oct 5, 2008 at 7:34 PM, Michael P. <baseball.mjp@gmail.com> wrote: >> Hi, >> >> How would I go about getting a random number that was in a specified range of 2 numbers? >> For example, getting a number inbetween 1000 and 2000. >> >> -Michael P. >> > > lo + rand() % (hi - lo) > > assuming you're using Phobos, where rand() returns a number in the > range [0, uint.max]. > > This will get you a number in the range [1000, 2000); that is, it will > be at least 1000 and at most 1999. If you need 2000 to be one of the > numbers generated, use 2001 as the hi. The random numbers will not be evenly distributed, though. You'll get more which are closer to 1000 than to 2000. (Imagine uint.max = 1000. Then 0 and 1000 map to 1000, but every other number has only one number which maps to it). Simple way to fix this is to ignore numbers from the non-uniform part: uint rmax = uint.max - (uint.max % (hi-lo)); uint r; do { r = rand(); } while (r>rmax); return lo + r % (hi - lo); | |||||||||||||
| |||||||||||||
