create zip file from multi-files ref: http://stackoverflow.com/questions/1754352/download-multiple-files-as-zip-in-php

zip-files.php

$files = array('readme.txt', 'test.html', 'image.gif');
$zipname = 'file.zip';
$zip = new ZipArchive;
//$zip->open($zipname, ZipArchive::CREATE); // the mode will append more files to existing file 
$zip->open($zipname, ZipArchive::OVERWRITE); // always create new file even file is existing

foreach ($files as $file) {
  // $zip->addFile($file); // original code if you want to keep original path of $file when extracting zipped file, means that $zip will create hierarchy folders contain the file
  $zip->addFile($file, basename($file)); // changed, if you want to zip all files in single folder
}
$zip->close();

header('Content-Type: application/zip');
header('Content-disposition: attachment; filename='.$zipname);
header('Content-Length: ' . filesize($zipname));
readfile($zipname);