Search $_POST array using strpos() - php

Question

Once a form is submitted I need to search through the POST array for words like 'ProductID' and store the name and the value in an associative array. I need to do this as you can list x amount of products through another page. So sometimes there's only 3 products listed, other times it's 10 and so on.
The HTML:
<div class="col-sm-3">
<label class="control-label">ADULT TRIP - $139</label>
<select class="form-control valid" name="ProductID-1">
<option value="-1">-- Please Select --</option>
<option value="0">0</option><option value="1">1</option>
<option value="2">2</option><option value="3">3</option>
</select>
</div>
What I've got so far in PHP:
foreach( $_POST as $value ) {
if (strpos($_POST,'ProductID') !== false) {
//Store in associative array
}
}
What I want to achieve is, once the form is submitted, loop through POST, check each item for the word "ProductID", if there's a match, store the name and value into an associative array. At the moment everything is returning true. Any help would be greatly appreciated.

Answer 1

Use:
foreach( $_POST as $key=>$value ) {
if (strpos($key,'ProductID') !== false) {
//Store in associative array
}
}
Instead:
foreach( $_POST as $value ) {
if (strpos($_POST,'ProductID') !== false) {
//Store in associative array
}
}

Answer 2

If you will have several ProductID I can use an array name="ProductID[1]" it will be easy then to manage your post

Answer 3

$ProductID= $_POST['ProductID'];
try echo $ProductID[0];

Answer 4

As pointed out by Ôrel I can use an array and loop through that as I see fit. I changed the HTML from:
<select class="form-control valid" name="ProductID-1">
to:
<select class="form-control valid" name="ProductID[<? echo $product_Results['ProductID']; ?>]">
Upon submitting the form, I changed my PHP to:
foreach( $_POST as $stuff ) {
if( is_array( $stuff ) ) {
foreach( $stuff as $ProductID => $qty ) {
echo 'product ID: '.$ProductID.' - qty: '.$qty.'<br />';
}
}
}
That way I can loop through the form until I find one that is the array (ProductID) and loop through that as an associative array. This allows me to get the Product ID as well as the quantity to go onto the next step.