Checks if the current post has any of given category.

The given categories are checked against the post’s categories’ term_ids, names and slugs.
Categories given as integers will only be checked against the post’s categories’ term_ids.

If no categories are given, determines if post has any categories.

function has_category( $category = '', $post = null ) {
	return has_term( $category, 'category', $post );
}