Add files to zip with php - php

Question

my php code for create zip file is:
function zipFilesDownload($file_names,$archive_file_name,$file_path)
{
$zip = new ZipArchive();
if ($zip->open($archive_file_name, ZIPARCHIVE::CREATE )!==TRUE) {
exit("cannot open <$archive_file_name>\n");
}
foreach($file_names as $files)
{
if (!file_exists($files)) { die($files.' does not exist'); }
if (!is_readable($files)) { die($files.' not readable'); }
$zip->addFile($file_path.$files,$files);
}
$zip->close();
header("Content-type: application/zip");
header("Content-Disposition: attachment; filename=$archive_file_name");
header("Pragma: no-cache");
header("Expires: 0");
readfile("$archive_file_name");
exit;
}
if ($act=="backup") {
$fileNames=array('us/man.txt');
$zip_file_name='myFile.zip';
$file_path=dirname(__FILE__).'/';
zipFilesDownload($fileNames,$zip_file_name,$file_path);
}
i add this code in my php, page show this code instead download:
PK0�~E1x��us/man.txtKIPK0�~E1x��users/mohammad-ali/mamad.txtPKJ>
but if i add it in another php, zip file downloaded correctly.