<?php if( has_post_thumbnail()) {
	$res = wp_get_attachment_url( get_post_thumbnail_id($post->ID) ); ?>
	<a title="<?php the_title() ?>" href="<?php the_permalink(); ?>"><img alt="<?php the_title() ?>" class="kresim" src="<?php echo $res ?>" width="100%" /></a>
<?php } else { ?>
<a title="<?php the_title() ?>" href="<?php the_permalink(); ?>"><img alt="<?php the_title() ?>" class="kresim" src="resim_adresi" width="100%" /></a>
<?php } ?>