I'm developing an app that manages Excel files so each user can open a different, serialized file.

It has to add zeros to a number at some point (so the filename becomes nicely formatted), so I've made this into a sub. This sub is called from another sub that starts the process of creating and opening the Excel documents.

So this is the sub who does the job:

sub geraNova
{
    my $ctrl = './control.dat';
    
    open(CTR, "+>>$ctrl");
    flock(CTR, 2);
    
    my $id = <CTR>;
    
    flock(CTR, 8);
    close(CTR);
    
    $id = $id + 1;
    
    unlink $ctrl;
    
    open(CTR, "+>>$ctrl");
    flock(CTR, 2);
    
    print CTR $id;
    
    flock(CTR, 8);
    close(CTR);
    
    $id = addZeros($id); 
    #The above calls the sub passing the id to format
    
    my $file = 'C:\Lobo\Sites\test'.$id.'.xls';
    
    my $Excel = Win32::OLE->GetActiveObject('Excel.Application') || Wi
+n32::OLE->new('Excel.Application');
    $Excel->{DisplayAlerts} = 0;
    $Excel->{Visible} = 1;
    
    my $Book = $Excel->Workbooks->Add();
    $Book->SaveAs($file);
    
    my $ActBook = $Excel->Workbooks->Open("$file") || die "Não foi pos
+sível abrir a planilha. Erro: $!";
    
    undef $Excel;
    undef $Book;
    undef $ActBook;
}
[download]

And this is the one who should add zeros to the control number wich was extracted from a text file:

sub addZeros
{
    my $num = $_; 
    
# Below is the line that I'm having problems. 
#Perl tells me: Use of uninitialized value in length

    while(length($num) < 6)
    {
        $num = "0".$num;
    }
    
    return $num;
}
[download]

I know I must be missing something very basic, but I still don't get it... Help, please.