Display one's search query

Ran into a new problem and I found out it has to do with my solution to the previous problem I had. To display the search query I did the following:

form code:
<form method="post" action="search.php">
<input type="text" name="tags,content,title_keyword" id="textfield" value="Search..." />
<button class="btn" title="Submit Search" name="submit"></button>

And in my search.php page I added the following line:
$searchquery = $_POST["tags,content,title_keyword"];


To display the results on search.php I use this code:
<h3>Search Results for "<?php echo $searchquery ?>"</h3><p></p>
<?php foreach ($articlesRecords as $record): ?>
Title: <?php echo $record['title'] ?><br/>
Category: <?php echo $numToName[$record['category']] ?><br/>
Tags: <?php echo $record['tags'] ?><br/>
_link : <a href="<?php echo $record['_link'] ?>"><?php echo $record['_link'] ?></a><br/>
<hr/>
<?php endforeach; ?>

<?php if (!$articlesRecords): ?>
No records were found!<br/><br/>
<?php endif ?>



The result is good, except for the category. The notice I get:

Notice: Undefined index: 2 in C:\xampp\htdocs\xampp\cmsbuilder\search.php on line 173

I found out that this has to do with the fact that I use $numToName, because I do get the result 2 (category 2) when I remove the $numToName part. Normally the $numToName function works fine though and it ALSO does in search.php if I delete $searchquery = $_POST["tags,content,title_keyword"];

Could anyone explain to me why the $numToName function doesn't work when I add the $searchquery = $_POST["tags,content,title_keyword"];
part? And even more important, does anyone have any suggestions on how to fix it?

Thanks again for your help :)

EDIT:
This is the code I use for $numToName at the top of my page:

$numToName=array();

foreach($categoryRecords as $record){
$numToName[$record['num']]=$record['name'];
}