Thanks guys, and in the meantime, I've finished the rest of the program. Seems to work perfectly and I'm gonna post it here for everyone to see (maybe it'll be useful to someone.. who knows). Also I'll take a look at what Bethany suggested. But for now, using arithmetic division and modulo worked xD Here's the code if anyone wants it. When running it from a command line type perl than whatever you name the file followed by arguments which go: IP address to subnet, current mask, number of hosts/subnets, "hosts" or "subnets" depending on what you want and in the end, the maximum number of subnets to display. It then displays the new mask, and the subnets including their first and last IP address.

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

sub bin_to_dec
{
    my $sum= 0;
    my $mult= 128;
    my $i;
    for $i($_[0] .. $_[1])
    {
        $sum+= $mult* $adress_bin[$i];
        $mult/= 2;
    }
    return $sum;
}

sub dec_print
{
    print bin_to_dec(0, 7), ".", bin_to_dec(8, 15), ".", bin_to_dec(16
+, 23), ".", bin_to_dec(24, 31);
}

sub num_of_bits
{
    my $i= 2;
    my $number= 2;
    while($number< $_[0])
    {
        $i++;
        $number= (2** $i)-2;
    }
    return $i;
}

$adress_dec= $ARGV[0];
$old_mask= $ARGV[1]-1;
$num_of= $ARGV[2];
$sub_host= $ARGV[3];
$max_to_show= $ARGV[4];

@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);

if($sub_host eq "hosts")
{
    $new_mask= 31- num_of_bits($num_of);
}
else
{
    $new_mask= $old_mask+ num_of_bits($num_of);
}

print "New mask: ", $new_mask+1, "\n\n";

$to_show= (2**($new_mask- $old_mask))-2;
if($to_show> $max_to_show)
{
    $to_show= $max_to_show;
}

for $i(1 .. $to_show)
{
    $temp= $i;
    $i2= $new_mask;
    while($temp!= 0)
    {
        $adress_bin[$i2]= $temp % 2;
        $i2--;
        $temp= int($temp/ 2);
    }
    for $i2($new_mask+1 .. 31)
    {
        $adress_bin[$i2]= 0;
    }
    dec_print();
    print "\n\t";
    $adress_bin[31]= 1;
    dec_print();
    print "\n\t";
    for $i2($new_mask+1 .. 31)
    {
        $adress_bin[$i2]= 1;
    }
    $adress_bin[31]= 0;
    dec_print();
    print "\n";
}
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