Selecting child pages with a specific parent page doesn't work - wordpress

Question

I need to add a specific function when child pages of a specific parent page are visualized.
My parent page has ID= 115 and it hase a 7 child pages. I used the following code
global $post; // load details about this page
if(is_page()&&($post->post_parent== '115)) {
echo ' This is a subpage';
}
else {
echo 'This is not a subpage';
}
Though it should work, the output echo, when I visualize one of the child pages, is "This is not a subpage" -> it means that it doesn't recognize it as a child page.
What is wrong? Thank you very much

Answer 1

Want to detect whether a specific Page on a WordPress has children or not?
This function comes in handy, just add it to your functions.php:
function has_subpage() {
global $post;
if($post->post_parent){
$children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0");
} else {
$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
} if ($children) {
echo ' This is a subpage';
} else {
echo ' This is a not subpage';
}
}

Answer 2

You can achieve the desired result by taking the following steps listed below...
Within your child theme, on your page.php first check if your are on a sub page via $post->post_parent.
Then within that, you can return an array of ancestors via get_post_ancestors
Then setup a condition to get the ID of the top level parent page
Once you have the ID, you can easily target the parent page by name. I recommend this so that when your theme travels for your development environment to our live environment, or if you had to manually create pages in any of these environments, the names will be the same.
Finally, enter your code for the sub page that targets its specific parent page location.
if (is_page() && $post->post_parent) :
$parents = get_post_ancestors($post->ID);
$id = ($parents) ? $parents[count($parents) - 1] : $post->ID;
$parent = get_post($id);
$parent_slug = $parent->post_name;
if ($parent_slug == "slug-of-your-specific-parent-page") {
//TEST
echo "this is custom text displaying on my sub page for a specific parent page";
//OR ADD YOUR SPECIFIC FUNCTION
...
}
endif;