Set 3 iframes in a row

Question

SCENARIO: I inherited a WordPress site that uses the Thesis theme. I have Content Blocks installed, which I use to populate the right sidebar. I have a function that randomly picks up three post excerpts in the Books category. The excerpts contain iframes to book listings from Amazon.com. View on http://thebakingwizard.com/

PROBLEM: The posts are picking up randomly, as desired, but the iframes are outside of the layer structure in the function.

WHAT I HAVE DONE SO FAR:

1. I understand that iframes should not be inside paragraph tags, so I used remove_filter( 'the_excerpt', 'wpautop' ); to remove the paragraph tags that Content Blocks create automatically. This did not change the situation.
2. I changed the unordered list HTML to divs in case they were causing the problem. This did not work either.

I need the iframes to be inside the divs so I can line them up in one row.

THE FUNCTION

function RandomBook() 
{ 
$args = array(
'post_type' => 'post',
'orderby'   => 'rand',
'posts_per_page' => 3,
'category_name' => 'Books',
);

$the_query = new WP_Query( $args );

if ( $the_query->have_posts() ) {

$string .= '<div id="AmazonListings">';
while ( $the_query->have_posts() ) 
{
    $the_query->the_post();
    $BookExcerpt = the_excerpt();
    $string .= '<div class="BookExcerpt">'.$BookExcerpt.'</div>';
} // end while
$string .= '</div><!-- end Amazon book listings -->';
/* Restore original Post Data */
wp_reset_postdata();
} else {

$string .= 'no posts found';
} // 5/23/17 Nora added */

return $string; 
} /* End Random post code from http://www.wpbeginner.com/wp-tutorials/how-to-display-random-posts-in-wordpress/<br />
 5/11/17 Nora added  */

add_shortcode('RandomBook','RandomBook');
add_filter('widget_text', 'do_shortcode'); 

Answer 1

The problem is that you are using the_excerpt(). This function prints out the excerpt immediately, it doesn't return a string.

From the core:

/**
 * Display the post excerpt.
 *
 * @since 0.71
 */
function the_excerpt() {

    /**
     * Filters the displayed post excerpt.
     *
     * @since 0.71
     *
     * @see get_the_excerpt()
     *
     * @param string $post_excerpt The post excerpt.
     */
    echo apply_filters( 'the_excerpt', get_the_excerpt() );
}

So you need to circumvent the echo by using apply_filters( 'the_excerpt', get_the_excerpt() ) instead of the_excerpt(), then you get the string you need, and the iframes should be where they belong.