Creating Find and Replace System in PHP

 Html code:-
--------------------------------

<form action ="findreplace.php" method="POST">

<textarea name="string" col="6" rows="5"></textarea><br><br>

Find <input type="text" name="find"><br><br>

Replace <input type="text" name="replace"><br><br>

 <input type="submit" value="Submit">

</form>

Php code:

----------------------------

<?php 

if (isset($_POST['string']) && isset($_POST['find']) && isset($_POST['replace'])){

 $string = $_POST['string'];

$find = $_POST['find'];

$replace = $_POST['replace'];

$offset=0;

$strlen = strlen($find);

if (!empty($string) && !empty($find) && !empty($replace) ) {

while($strpos = strpos ($string, $find, $offset)){

}

$offset = $strpos + $strlen;

$string=substr_replace ($string, $replace, $strpos, $strlen);

echo $string;

}else{

echo "Fill up all fields!";

}

}

?>