How to get the category id of the current post?

Question

PHP

How to get the category id of the current post? The below function does not work, I use it in a while loop.
$category = get_the_category(the_ID());

Answer 1

$category = get_the_category(get_the_ID());
$cat_id = get_cat_ID($category[0]->cat_name);
echo $cat_id;

Why do you need these extra steps?

$categories = get_the_category(); // Внутри цикла
$cat_id = $categories[0]->cat_ID // ID самой категории
$parent_id = $categories[0]->category_parent // ID категории-родителя, если нужен

Answer 2

get_the_category($post->ID)[0]->term_id