Do not initialize your $max_number:

my $max_number;        #initialize a variable that keeps the maximum n
+umber
[download]

so you can check for undef in your loop:

if(!defined($max_number) or $current_number > $max_number)            
+    
    {
        $max_number = $current_number;            #compare each time t
+he number we have in the line with the max number    
    }
[download]