Code for bootstrap 3 responsive navbars in wordpress using wp-bootstrap-navwalker class

bs3-version.php

<?php 

/**
 * The register_nav_menus call should go inside your themes setup function 
 * (usually found inside functions.php).
 */
register_nav_menus(
   array(
	   'footer_nav' => __( 'Footer Menu', 'mytheme' ), // example of adding a menu location
	   'top_menu'   => __( 'Top Menu', 'mytheme' ), // we will be using this top_menu location
   )
);

/**
 * The require_once should go inside your functions.php file and needs to point
 * to the directory where the wp-bootstrap-navwalker.php file has been placed 
 * insisde your theme.
 */

// Register Custom Nav Walker Class
require_once 'wp-bootstrap-navwalker.php';

// The code below goes into your header.php file. It is a mix of html and php. ?>
<nav class="navbar navbar-default" role="navigation">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
        <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-ex1-collapse">
            <span class="sr-only">Toggle navigation</span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
        </button>
    <a class="navbar-brand" href="#"><?php esc_html_e( get_bloginfo('name') ); ?></a>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse navbar-ex1-collapse">
        <?php
        wp_nav_menu( array(
            'menu'        => 'top_menu',
            'depth'       => 2,
            'container'   => false,
            'menu_class'  => 'nav navbar-nav',
			// if no menu is assigned to this slot use the fallback defined by the walker.
            'fallback_cb' => 'WP_Bootstrap_Navwalker::fallback',
            // Process nav menu using our custom nav walker.
            'walker'      => new WP_Bootstrap_Navwalker(), 
	) );
        ?>
    </div><!-- /.navbar-collapse --> 
</nav>