I have a question about rand() ... I have the following code:

#!/usr/bin/perl

my @arr = ();
my $counter = 1;

for($i=0; $i<32; $i++) {
    while(1) {
        $rand = int(rand(32));
#            print "testing: $rand\n";
        if (grep(/$rand/, @arr) == 0) {
            print "$counter: $rand\n";
            push @arr, $rand;
            $counter++;
            last;
        }
    }
}

[download]

The goal is to produce random numbers from 0 to 32, but the sequence has to be without repeating any number, whenever I run this code I always get 23 or 24 numbers, after this the computer keeps generating numbers but I can't make the computer generate the last random numbers.

Any ideas?

I ran the code under Fedora, Cygwin and Active Perl but I get the same behavior on all platforms.

This is the output I get:

$ ./create_random_numbers.pl 
1: 29
2: 20
3: 27
4: 31
5: 25
6: 21
7: 19
8: 13
9: 26
10: 12
11: 8
12: 28
13: 11
14: 16
15: 22
16: 17
17: 4
18: 10
19: 23
20: 18
21: 24
22: 15
23: 14
24: 30

[download]

After this the scripts "hangs" and the CPU goes to almost 100% usage, I have it running for more that 5 minutes but no luck (I am not expecting to run scripts for more than 5 minutes just to generate random numbers)

Update

Thanks for all the replies what I was looking for is what almut wrote, that little part of the regexp made the difference (/^$rand$/). Although I think the idea of using shuffle is good, I never work with that module before. I think basically now I have my own version of shuffle.

Now my next task will be to test the performance using shuffle and using rand, I will see what is faster.

My final code looks like this: 

#!/usr/bin/perl

my @arr = ();
my $counter = 1;
my $range;

for($i=0; $i<$range; $i++) {
    while(1) {
        $rand = int(rand($range));
        if (grep(/^$rand$/, @arr) == 0) {
            print "$rand\n";
            push @arr, $rand;
            $counter++;
            last;
        }
    }
}

[download]

In reply to How much random is rand()? by gmoque

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