Trying to understand The Loop and the $post – Variable

Hi,

I thought that I understand the loop, but obviously I don’t.

On many of my websites I use quite many loops.

My first question is:
What is the difference between the “2 Main Loop Techniques” – “get_posts()” and “query_posts()” ?
Is there any difference at all?

I think I’ve figured out some conflicts especially with conditional tags:
I have one “Main-Loop” on my page that is displayed, let’s say it’s a single article (single.php).
Under the single article I want to display some “Related Articles”. I do this with a simple “query_posts()” loop.

<?php
//first loop
while (have_posts()) : the_post();
  // the content of the post
  the_content('');
endwhile;

//second loop
rewind_posts();
$related_query="cat=".$cat-var."&showposts=3";
query_posts($related_query);
while (have_posts()) : the_post();
  // the title of the related post
  the_title('');
endwhile;
?>

OK. Let’s assume that the post in Loop 1 and Loop 2 are in different categories. And let’s assume that I want to use the conditional Tag “in_category()” in the sidebar.

I would expect the “in_category()” tag to output TRUE for the “ORIGINAL POST’S” category (Loop #1).

But it outputs TRUE for the last post in Loop #3. This is comprehensible, but in my opinion not the proper solution.

Is there any workaround for that?

Of course, I could do something like

$myposts = get_posts('numberposts=5&offset=1&category=1');
foreach($myposts as $alternativepost) : ?>
    <li><a href="<?php echo $alternativepost->guid; ?>"><?php echo $alternativepost->post_title/?></a></li>
<?php endforeach; ?>

But as you see, I cannot use many template tags anymore with this workaround.

It is a very tricky issue and I think I’m just starting. I hope, I expressed clearly what I want to show.
It’s just about making a simple, “clean” loop without always affecting and overwriting the $post – variable.