use Excerpt just in categories of wordpress theme

<?php get_header(); ?>
 


<div id="content">

    <div id="main" role="main">
        <?php get_template_part('loop'); ?>
    </div>
   
    <?php get_sidebar(); ?>
   
</div>
<div class="clear"></div>

<?php get_footer(); ?>

<?php
 
    while (have_posts()) : the_post();  ?>
 
    <div id="post-<?php the_ID(); ?>" class="post clearfix">
        <div class="post-content">

            <h2 class="title"><a href="<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'wpzoom' ), the_title_attribute( 'echo=0' ) ); ?>" rel="bookmark"><?php the_title(); ?></a></h2>
           
            <div class="top-meta">
                 <?php if (option::get('display_date') == 'on') { ?><span class="date"><?php printf( __('%s at %s', 'wpzoom'),  get_the_date(), get_the_time()); ?></span><?php } ?>
                 <?php edit_post_link( __('Edit', 'wpzoom'), '<span>', '</span>'); ?>
              </div><div class="clear"></div>
           
            <div class="entry">
                <?php if (option::get('display_content') == 'Full Content') {  the_content(''); } else { the_excerpt(); } ?>
                 
                   <div class="clear"></div>
            </div><!-- /.entry -->
        </div><!-- /.post-content -->
        <div class="clear"></div>

        <div class="post-meta clearfix">  
       
            <?php if (option::get('display_share') == 'on') { ?>
               
            <?php } ?>
           
            <?php if (option::get('display_readmore') == 'on') { ?><span class="readmore"><a href="<?php the_permalink() ?>"><?php _e('بیشتر بخوانید', 'wpzoom'); ?></a></span><?php } ?>          

            <?php if (option::get('display_comments') == 'on') { ?><?php comments_popup_link( '0', '1', '%', 'comments', __('Comments Off', 'wpzoom')); ?><?php } ?>
             
          </div>
       
    </div><!-- #post-<?php the_ID(); ?> -->
   
 
<?php endwhile; ?>
<?php get_template_part( 'pagination'); ?>
<?php wp_reset_query(); ?>

function trim_title() {
$title = get_the_title();
$limit = "200";
$pad="...";

if(strlen($title) <= $limit) {
echo $title;
} else {
$title = substr($title, 0, $limit) . $pad;
echo $title;
}
}