how to fix php $referenceNo = strtoupper($_POST['referenceNo']); code example

Example 1: php uppercase

//string to all uppercase
$string = "String with Mixed use of Uppercase and Lowercase";
//php string to uppercase
$string = strtoupper($string);
// = "STRING WITH MIXED USE OF UPPERCASE AND LOWERCASE"

Example 2: strtoupper

<?php
echo strtoupper("Hello WORLD!");
?>