question on rand()

[Anna Sidera]

The following program:

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>

int main()
{

int i=0;
int j=rand();
while (rand()!=j) i++;
printf("%d\n",i);

return 0;
}



gives the following output:

-1406966551



>From this, can I find out when the numbers start repeating? How can I find it? I cannot find the period using

man rand



Anna
----- Original Message -----
From: Marc Glisse <marc.glisse@inria.fr>
Date: Saturday, August 6, 2011 7:34 pm
Subject: Re: question on rand()

> On Sat, 6 Aug 2011, Andrew Haley wrote:
> 
> > On 08/06/2011 08:47 AM, Anna Sidera wrote:
> >> Hello,
> >>
> >> I am using gcc on a unix machine. Can you tell me how many 
> random numbers can be generated using
> >>
> >> rand()
> >>
> >> before the random numbers start repeating?
> 
> man rand
> If it's not there, complain to your unix vendor.
> The period is required by posix to be larger or equal to 2^32.
> 
> > One would hope it has full period, i.e. it generates all 
> RAND_MAX numbers,
> > but that depends on your system.
> 
> One would even hope the period is larger, so the output of rand() 
> is not a 
> deterministic function of its last return value (random generators 
> often 
> keep a hidden state).
> 
> -- 
> Marc Glisse
>