Exclude categories from the Loop?

see https://codex.www.ads-software.com/Template_Tags/query_posts

insert before WordPress loop

<?php query_posts(cat='-6,-12,-15'); ?>

will remove categories 6, 12, 15 from displaying in the loop

Thank you for your reply, stvwlf.

The thing is – I made several if(is_category) loops in my category.php file. Well, see for yourself:

<?php if ( is_category(1) ) : ?>
      <div id="contentLeftCategory">
      <h1>Category 1</h1>
<?php query_posts('cat=1'); ?>
<?php if(have_posts()) : while(have_posts()) : the_post(); ?>
       <div <?php post_class() ?> id="post-<?php the_ID(); ?>">
        <h3><a href="<?php the_permalink() ?>" rel="bookmark" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a></h3>
        <span class="contentLeftPostMeta"><?php the_time('j. F, Y.') ?> | <?php the_category(', ') ?> | <?php comments_popup_link('No comments', '1 comment', '% comments'); ?>
</span>
       </div><?php endwhile; ?>

<?php next_posts_link('? Older') ?>
<?php previous_posts_link('Newer ?') ?>
<?php else: ?>
<h3>Content not available</h3>
<p>The content you are looking for is currently not available</p>
<?php get_search_form(); ?>

		<?php endif; ?>
	<?php endif; ?>

There are about six of these loops. And yes, my knowledge of PHP is limited. ??

I want to avoid the category-id files. So, what I need is a function that displays the default loop if I’m not on one of these categories (11, 16, 21, 12). But, if I do browse one of these categories the loop is disabled.

please paste the entire code of category.php in a pastebin
https://wordpress.pastebin.ca/ and post the URL here

I can’t tell from your code fragment what you are doing or what you are trying to do.

https://wordpress.pastebin.ca/1451285

This is the category.php file. There is some text in my native language tho, sorry for that.