Separating values from XML using php with xpath

I need help from selecting data from XML. I can't seem to figure out the way xpath works with specific data selecting. Here is my XML:

<?xml version="1.0"?>
<a>
<b>
    <c>Value 1</c>
    <d>Value 2</d>
</b>
<b>
    <c>Value 3</c>
    <d>Value 4</d>
</b>

And PHP code i'm trying to use would be:

<?php
$xml = simplexml_load_file("xml.xml"); 

$result = $xml->xpath('b/c | b/d');
foreach ($result as $val){
echo $val['c'] . $val['d'] . "<br>;
}

If i echo $val, i get all values, however, i want to separate it so i have $val['c'] and $val['d'], like when selecting specific data from MySQL table. Thank you in advance