Customizing Search Queries

Hi,

I am trying to modify the default search results in my site.

There is a category called news.

When I am searching while from the news archive page or a news post then it should show results only from news category.

When I am searching from rest of the site, it should show results excluding the news. I am using a flag to detect the source page to detect if it was a news page or not. If it is a news page then the flag $is news would become 1 and if not it would be 0. But, somehow it is not setting the value and it is taking the default value 0.

Setting the flag is done by a function call
set_is_news(0);

This is the following code in functions.php

global $is_news;
$is_news=0;

function set_is_news($value) {
	global $is_news;
	$is_news=$value;
}

function exclude_category( $query ) {
// The category_id is 1 for news
	global $is_news;
	if ( $query->is_home) { $is_news=0;}
    if ( $query->is_search ) {
	if ($is_news==1)
		$query->set( 'cat', '1' );
	else
		$query->set('cat', '-1' );
		$query->set('post_type', 'post');
	}
}

add_action('pre_get_posts','exclude_category');