How to display posts of a particular category in php?

Question

The problem here is , when i type cat='hotels' manually , it displays the detail of that category .
But when i give cat=$category , (category will be selected by user) , it says that category is undefined variable .

What i want is , when i click on any category , the posts related to that category should get displayed .

Do help to solve this .

Below is the code .

Here's the script .

<script>
   $(document).ready(function(){
   $(".button").click(function(){
   $("#display").load("cat.php");
   });
   });
</script>  

Here's my html.

<ul>            
<li class="button"><a href="#">Hotels</a></li>
<li class="button"><a href="#">Resorts</a></li>
<li class="button"><a href="#">Hills</a></li>
</ul>

<div id="display"></div>

This is my insert.php file.

$id = isset($_POST['post_id'])?$_POST['post_id']:'';
$category=$_POST['cat'];

mysql_connect('localhost','root','');

mysql_select_db("database") or die("Unable to select database");

$insertquery="INSERT INTO posts VALUES('$id','$category')";

$result=mysql_query($insertquery);

if(! $result )
{
  die('Could not enter data: ' . mysql_error());
}
else {

        echo "Entered data successfully\n";
        header('Location:home.php');
    }   

mysql_close();
?>    

This is the code (cat.php) to display it on my home page.

<?php
$row="";

$link = mysql_connect("localhost","root","");
mysql_select_db("database");

$query = "SELECT * FROM posts WHERE cat=$category";

$result = mysql_query($query) or die("Query to get data failed with error:   ".mysql_error());


while($row = mysql_fetch_array($result)) { 

echo    $row['cat'];

}
mysql_close($link);
?>

Answer 1

Change

$query = "SELECT * FROM posts WHERE cat=$category";

To

$query = "SELECT * FROM posts WHERE cat='$category'";