sample.phtml

<form role="search" method="get" class="search-form" action="<?php echo home_url( '/' ); ?>">
	<label>
		<span class="screen-reader-text"><?php echo _x( 'Search for:', 'label' ) ?></span>
		<input type="search" class="search-field" placeholder="Search..." value="<?php echo esc_attr( get_search_query() ); ?>" name="s" title="<?php echo esc_attr_x( 'Search for:', 'label' ); ?>" />
	</label>
	<?php
		// output all of our Categories
		// for more information see http://codex.wordpress.org/Function_Reference/wp_dropdown_categories
		$swp_cat_dropdown_args = array(
				'show_option_all'  => __( 'Any Category' ),
				'name'             => 'swp_category_limiter',
			);
		wp_dropdown_categories( $swp_cat_dropdown_args );
	?>
	<input type="submit" class="search-submit" value="Search" />
</form>