Update: except that you'd have to do $binnumb = $binary . $binnumb instead, which will get a warning unless you initialize $binnumb to '' at the start. And you need to handle negative numbers.

Yea I realize I have to handle negative numbers still. I did get it to work with a while loop like this:

sub dec2bin {
    my $binnumb;
    while($inNumber > 0) {
    my $binary = $inNumber % 2;
    print $inNumber; print "\n";
    $inNumber = int($inNumber / 2);
    $binnumb .= $binary; 
    print $binnumb; print "\n";
    }
    $binnumb = reverse $binnumb;
    return $binnumb;
    }
[download]

I wasn't thinking when I tried to do it with an if statement. I don't get any errors with this and it gives me the right number. I just didn't understand the code that you gave me at first. What does %b do?

%b formats a number as binary (but first casts it to an unsigned value, so you'd need to make sure you only feed it positive values):

$ perl -we'printf "%b", 123'
1111011
[download]

(printf outputs directly, sprintf returns a formatted string).

Looks like your code above will give undef for 0; I think that could be fixed by changing your while () {} do a do {} while ().