From: elric AT wheel DOT dcn DOT davis DOT ca DOT us (Jeffrey Taylor)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Randomization of Numbers with rand() and stdlib.h
Date: 30 Sep 1996 16:00:55 GMT
Organization: Davis Community Network - Davis, California, USA
Lines: 31
Message-ID: <52oqrn$ml@mark.ucdavis.edu>
References: <19960930 DOT 074610 DOT 11630 DOT 0 DOT wilbur3 AT juno DOT com>
NNTP-Posting-Host: wheel.dcn.davis.ca.us
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Will C Stockwell (wilbur3 AT juno DOT com) wrote:
:    I am trying to randomize numbers between 0 and 15. But when I use the
: stdlib.h file and the rand() function. I get the same number every time.
: It's something like 25049302. Really long. I have set the RAND_MAX macro
: value to 15 with a define statement but I still get the 25049302. Is
: their another way to get random numbers? With time as a random factor
: maybe? Thanks.
: 

You are using the RAND_MAX macro the wrong way around.  It tells you what 
the maximum value of rand() is.  From your problem description, I expect 
you are calling rand() once per program run.  Rand() returns values in a 
psuedo-random sequence.  To start at a different place in the sequence 
use srand() first.  A typical way to do this is :

#include <time.h>

   .
   .
   .

   srand(time(0));
   x = rand();

The easy way to get numbers in the range 0 to 15 is (rand() % 16) or the 
slightly faster (rand() & 0xF).

There was an article in Dr. Dobbs on getting truely random numbers.  Too 
much run time for most uses, but useful ideas in the pieces.

Jeff T