• Michael P. (4/4) Oct 05 2008 Hi,
• Jarrett Billingsley (7/11) Oct 05 2008 lo + rand() % (hi - lo)
• Don (12/29) Oct 09 2008 The random numbers will not be evenly distributed, though. You'll get

Michael P. <baseball.mjp gmail.com> writes:

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.

"Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:

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.

Don <nospam nospam.com.au> writes:

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);