I am not sure exactly what you are trying to do but as has been mentioned File::Find is the right tool for this job. This is some untested code for your pleasure...

use strict;
use warnings;
use File::Find;

my $starting_dir = "put path to dir here";

my $count_dat_png = 0;

find(\&wanted, $starting_dir);
print "number of dat and png files: $count_dat_png\n";


sub wanted
{
    return if -d ; # skip directories
                   # . and .. are directories
                   # or just leave this out entirely
        
    if (-f and ( /\.dat$/i or /\.png$/i))
    {
        #print "$File::Find::name\n"; #full name if you want
        $count_dat_png++;
    }
}
[download]

added: I would read the example and explanation of the module File::Find carefully.