post to subcategory and parent in wp_insert_post

this code works fine. the problem i have is that when i submit it only checks the parent category not the subcategory even though i specified both a parent and a subcategory.

please. what am i doing wrong.
ohh if you look in the html chunk, the 7 is parent cat and the numbers after the comma are the subcategories.

   <?php 
if(isset($_POST['new_post']) == '1') {
    $post_title = $_POST['post_title'];
    $post_category = $_POST['cat'];
    $post_content = $_POST['post_content'];
    $new_post = array(
          'ID' => '',
          'post_author' => $user->ID, 
          'post_content' => $post_content,
          'post_title' => $post_title,
          'post_status' => 'publish',
          'post_category' => array($post_category)

        );

    $post_id = wp_insert_post($new_post);

    // This will redirect you to the newly created post
    $post = get_post($post_id);
    wp_redirect($post->guid);
}      
?>

this is the html

<form method="post" action="" name="" onsubmit="return checkformf(this);">


<input type="text" name="post_title" size="45" id="input-title"/>

<textarea rows="5" name="post_content" cols="66" id="text-desc"></textarea></br>


<ul><select name='cat' id='cat' class='postform' > 
    <option class="level-0" value="7,95">child cat1</option> 
    <option class="level-0" value="7,100">child cat2</option> 
    <option class="level-0" value="7,101">child cat3</option> 
    <option class="level-0" value="7,94">child cat4</option> 
</select> 
</ul>

<input type="hidden" name="new_post" value="1"/> 

<input class="subput" type="submit" name="submitpost" value="Post"/> 


</form>

please let me know if you need more information. thanks in advance

Solutions Collecting From Web of "post to subcategory and parent in wp_insert_post"

The problem is, you can’t make an array like that in PHP. Trying to cast a string that contains a comma separated list as an array just produces an array with a single value–your comma separated string.

You want to use php’s explode function to create the array. It takes a string an splits it into a bona fide array based on an arbitrary delimiter (in your case, we’ll use a comma).

Try something like this:

if(isset($_POST['new_post']) == '1') {
    $post_title = $_POST['post_title'];
    $arr_post_category = explode(',',$_POST['cat']); // EXPLODE!
    $post_content = $_POST['post_content'];
    $new_post = array(
          'ID' => '',
          'post_author' => $user->ID, 
          'post_content' => $post_content,
          'post_title' => $post_title,
          'post_status' => 'publish',
          'post_category' => $arr_post_category // NOW IT'S ALREADY AN ARRAY

        );

    $post_id = wp_insert_post($new_post);

    // This will redirect you to the newly created post
    $post = get_post($post_id);
    wp_redirect($post->guid);
}