Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!jhunix!barrett
From: barrett@jhunix.HCF.JHU.EDU (Dan Barrett)
Newsgroups: comp.sys.amiga.tech
Subject: Re: rand() within a range.
Message-ID: <7083@jhunix.HCF.JHU.EDU>
Date: 7 Dec 90 21:41:28 GMT
References: <666@sheoak.bcae.oz>
Organization: The Johns Hopkins University - HCF
Lines: 47


I tried e-mail but it bounced.

In article <666@sheoak.bcae.oz> 737104@sheoak.bcae.oz (David Thiele) writes:
>Is there a way to generate random numbers within a certain range in
>Lattice C??

	It can be done in ANY language -- there is a mathematical formula
for it.  All you need is a function Rand() that returns a random real number
between 0 and 1 (not including 1).  This is commonly supplied by your
compiler company.

To generate a random integer between integers A and B, with A < B:

(1)	Figure out the distance between A and B:

		distance = B - A + 1;

(2)	Multiply a random number by the distance, and truncate the
	remainder.  This gives you a random integer between 0 and
	(distance - 1):

		first = floor(distance * Rand());

(3)	Now increase this number by A, to give you an integer between
	A and (A + distance - 1).  But remember:

		A + distance - 1
			= A + (B - A + 1) - 1
			= B

	So you have a random integer between A and B:

		answer = first + A;

Here is the final formula:

		answer = floor((B - A + 1) * Rand()) + A;

                                                        Dan

 //////////////////////////////////////\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
| Dan Barrett     -      Systems Administrator, Computer Science Department |
| The Johns Hopkins University, 34th and Charles Sts., Baltimore, MD  21218 |
| INTERNET:   barrett@cs.jhu.edu           |                                |
| COMPUSERVE: >internet:barrett@cs.jhu.edu | UUCP:   barrett@jhunix.UUCP    |
 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\/////////////////////////////////////