Add code to header or footer of WordPress

custom-header-footer.php

<?php
/**
 * Plugin Name:       My Custom Header Footer
 * Plugin URI:        http://fullworks.net/wordpress-plugins
 * Description:       Custom header Footer code
 * Version:           1.0
 * Author:            Fullworks
 * Author URI:        http://fullworks.net/
 *
 */
if ( ! defined( 'WPINC' ) ) {
	die;
}
add_action( 'wp_head', function() {
  /** add the code you want to output in the header between ?>   and <?php  e.g.
  *   ?>
  *   <script>
  *      alert('It Works!');
  *   </script>
  *
  */
  
  ?>

  <?php 
});

add_action( 'wp_footer', function() {
  /** add the code you want to in the footer output between ?>   and <?php  e.g.
  *   ?>
  *   <script>
  *      alert('It Works!');
  *   </script>
  *
  */
  
  ?>

  <?php 
});