Thread: Any way to set peramiters for rand() to return?

Please read the tutorials before posting!...

Originally Posted by ashinms

I'm trying to write a simple program that has the function rand() to assign a number between 1 and 100 to int x. Right now, the only way I can get this to happen, is to have the program to check x after it is set, and if it is above 100, "try again". Can I tell rand() to simply "not return above 100". It would be a 'much' more efficent technique

The tutorial that Sipher linked to suggests a technique that can introduce some bias, but it may still be acceptable for you. I suggest reading Prelude's article on using rand() for elaboration and alternatives.

The method that I prefer is a variant of the rejection method that you have in mind (and which Prelude mentions in her article):

Code:

const int range_min = 1;
const int range_max = 100;
const int range_size = range_max - range_min + 1
do
{
    n = rand();
}
while (n >= (RAND_MAX / range_size) * range_size);
n = n % range_size + range_min;

If they are available to you, you can also use the pseudorandom number generator facilities from the TR1 extension to the standard library.