Select Featured Category

Hi, i am developing my own theme and i want to create a slide show which will show all the post from a single categories.
I am using the code below for this
<?php $wp_query = new WP_Query( cat=2′);?>
<?php if(have_posts()) : while ( have_posts() ) : the_post(); ?>
<a href=”<?php the_permalink();
the_post_thumbnail(‘slide’); ?>
<?php endwhile;?>
<?php endif;?>`

But here i am selecting the category id manually in the loop is there any way to let the user select the category from the dashboard?