#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $path = shift || '.';

print Dumper traverse($path);

sub traverse {
    my ($path) = @_;

    my @files = `find $path -name '*.c' -o -name '*.txt'`;

    return if not -d $path;
    opendir my $dh, $path or die;
    while (my $sub = readdir $dh) {
        next if $sub eq '.' or $sub eq '..';
        traverse("$path/$sub");
    }
    close $dh;
    chomp @files;
    return \@files;
}

__DATA__

$ perl file.pl
$VAR1 = [
          './counts.txt',
          './file.txt',
          './sample.c',
          './testDir/anotherSample.c',
          './test.txt'
        ];