$post_per_page = 7;
$args = "";
$args .= "posts_per_page=" . $post_per_page;
if (isset ( $_GET[ 'category' ] ) ) {
$cat_names = array();
foreach ( $_GET[ 'category' ] as $value ) {
$cat_names[] = sanitize_key( $value );
}
$args .= "&category_name=" . implode("," , $cat_names);
}
$total_post = new WP_QUERY( $args );
$max_pages = $total_post->max_num_pages;
if ( $max_pages < get_query_var('paged') ) {
set_query_var('paged' , $max_pages ) ;
}
$current_page = (get_query_var('paged')) ? get_query_var('paged') : 1;
$args .= "&paged=" . $current_page;
query_posts( $args );