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How To Stop Variable From Resetting After Form Submit?
session_start();

include_once('db.php');

$cat_SQL = 'SELECT * FROM categories ORDER BY id';
$cat_RESULT = mysql_query($cat_SQL, $conn);
$cat_ROWS = mysql_fetch_assoc($cat_RESULT);
$cat_ROWS_number = mysql_num_rows($cat_RESULT);

if (is_null($category) || empty($category)) {
    $category = 1;
}

if (isset($category)) {
    if ($category < $cat_ROWS_number) {
        $category = $category + 1; echo $category;
    }
}

if (!isset($_SESSION['category'])) {
  $_SESSION['category'] = 1;
  $category = $_SESSION['category'];
}
else {
      if($_SESSION['category'] < $cat_ROWS_number) {
          $_SESSION['category']++;
          $category = $_SESSION['category'];
      }
}

if(isset($_SESSION['category']))
    $category = $_SESSION['category'];

$_SESSION['category'] = $category;