Display parent page only on sub-page wordpress

Question

I want to display parent page only on sub-pages. I am using this code but it display parent page on every page.

 <?php
$parent_title = get_the_title($post->post_parent);
echo $parent_title;
?>

Answer 1

you should try this function to check the parent child relation

function is_child($pageID) { 
global $post; 
if( is_page() && ($post->post_parent==$pageID) ) {
           return true;
} else { 
           return false; 
}
}

and use it like that

if(is_child(123)) { //parent id
  $parent_title = get_the_title($post->post_parent);
  echo $parent_title;
 }

Answer 2

you can try this

<?php 
if($post->post_parent>0)
{
$parent_title = get_the_title($post->post_parent);
echo $parent_title;
}
?>