Echo something with PHP code in the xml file

I am a novice and I work in PHP. And I do not know anything about xml. My English is not very good. If you see a typo, please edit it

Please see the code below

<?php 
header("Content-type: text/xml");
$array = ["a", "b", "c"];
echo $array[0];

There is a problem with the output and I can not use the echo. The photo below is my output

please guide me

Answer

I found out from the url that you want to create a sitemap. You should see the output inside a xml code. for example:

<?php 
header("Content-type: text/xml");
$array = ["a", "b", "c"];

echo "<?xml version='1.0' encoding='UTF-8'?>"."n";
echo "<urlset xmlns='http://www.sitemaps.org/schemas/sitemap/0.9'>"."n";
 echo "<url>";
 echo "<loc>".$array[0]."</loc>";
 echo "<lastmod>".$array[1]."</lastmod>";
 echo "<changefreq>daily</changefreq>";
 echo "</url>";
echo "</urlset>";