StringsInPHP - //Problem 3. Find All Matches

//Problem 3.    Find All Matches
//Write a script that finds how many times a substring is contained in a given text (perform case insensitive search).
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
        <form method="post" action="FindAllMatches.php">
            <input type="text" name="str1">
            <input type="text" name="str2">
            <input type="submit" value="GO">
        </form>
    </body>
</html>
<?php
$string=(string)$_POST['str1'];
$substring=(string)$_POST['str2'];
$occurrences=substr_count($string, $substring); // 2
echo "The substring \"$substring\" is countained $occurrences times";
?>