How can PHP developers ensure that files and directories created by their scripts are easily manageable and deletable using external FTP programs?

PHP developers can ensure that files and directories created by their scripts are easily manageable and deletable using external FTP programs by setting the correct permissions on the files and directories. This can be achieved by using the `chmod()` function in PHP to set the appropriate permissions for the files and directories, allowing external FTP programs to have the necessary access to manage and delete them.

// Create a directory with permissions set to 0755
$dir = 'new_directory';
mkdir($dir, 0755);

// Create a file with permissions set to 0644
$file = 'new_file.txt';
$handle = fopen($file, 'w');
fclose($handle);
chmod($file, 0644);