Get the list of categories to which the article belongs

index.php

 <?php // Get the list of categories to which the article belongs

    $categories = get_the_category(); 
    $separator = ", ";
    $output = '';

    if($categories) {
        foreach($categories as $category) {
            $output .= '<a href="'.
            get_category_link($category->term_id).'">'.
            $category->cat_name .'</a>'.$separator;
            // $output .= $category->cat_name . $separator;
        }
    }
    echo trim($output, $separator);
?>