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From: jas@ISI.EDU (Jeff Sullivan)
Newsgroups: comp.lang.perl
Subject: random numbers?
Message-ID: <16698@venera.isi.edu>
Date: 8 Feb 91 22:11:33 GMT
Sender: news@isi.edu
Distribution: comp
Organization: USC-ISI
Lines: 92


Is there some problem with perl's srand and rand functions?

I wrote this program which is supposed to generate a random number
between 1 and 20, ecept if it produces a 10 on the first (and
subsequent) try, in which case it adds the first  (and subsequent) 10s
to another random number between 1 and 20.  

This is the code:

#!/usr/bin/perl
srand;

$total = $roll = int(1+rand(20));

while ($roll == 10) {
        $roll = int(1+rand(20));
        $total += $roll;
}

print $total,"\n";


I wrote a test program to run this a lot of times in a row to test it.
Here's the program:

#!/usr/bin/perl
foreach (0..$ARGV[0]) {
        print `roll`;
}

Here's the output:

17
7
7
7
18
18
8
18
19
19
9
9
19
19
19
*24
*24
*24
20
20
20
20
20
20
*25
*25
*25
*25
*25
*25
20
20
20
20
11
11
11
11
11
1
1
1
1
1
11
11



Hardly looks random to me.

What am I doing wrong?

jas
--
--------------------------------------------------------------------------
Jeffrey A. Sullivan		| Senior Systems Programmer
jas@venera.isi.edu		| Information Sciences Institute
jas@isi.edu                    	| University of Southern California