Hello, I've decided to write a program which takes an IP address, its subnet mask and a number of hosts or subnets needed and generates a new subnet mask an prints out all of the subnets available with the new mask. I don't need help with the entire program, since I've already done it in C++ but I'm having some trouble with writing it in Perl.

The problem is that I get an error saying "Modification of non-creatable array value attempted, subscript -33" at line 8. I know that this happens if you try to modify an element of an array under a negative index, but $position is either 31, 23, 15 or 7 (at the start and shouldn't get any lower than 0 if it starts as 7). I don't know what's wrong. Here's all the code I've written until now. It's only supposed to take an IP address in x.x.x.x format and print it as a sequence of 32 bits.

sub dec_to_bin
{
    my $number= $_[0];
    my $position= $_[1];
    while($number!= 0)
    {
        $adress_bin[$position]= $number % 2;
        $position--;
        $number/= 2;
    }
}

$adress_dec= "192.168.0.0"; # $adress_dec= $ARGV[0];
$old_mask= 16; # old_mask= $ARGV[1];
$num_of= 100; # num_of= $ARGV[2];
$sub_host= "host"; # sub_host= $ARGV[3];

@adress_dec= split(/\./, $adress_dec);

for $i (0 .. 31)
{
    $adress_bin[$i]= 0;
}

dec_to_bin($adress_dec[3], 31);
dec_to_bin($adress_dec[2], 23);
dec_to_bin($adress_dec[1], 15);
dec_to_bin($adress_dec[0], 7);

for $i (0 .. 31)
{
    print $adress_bin[$i];
}
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