更新数据WHERE

I have a table called client and I am trying to update the contact number, but for only the id that is typed in. I have a form that creates two textfields for the data to be changed. My problem is im unsure on how i can only update data for only the id that is entered.

Code:

<form method="post" name="update" >
Client ID:
<br>
<input type="text" name="clientid"><br>
Contact Number:
<br>
<input type="text" name="contactno"><br>
<input type="submit" name="submit" value="Update"><br><br>
</form>
<?php
if(isset($_POST['submit'])){
$client = $_POST['clientid'];
$contact = $_POST['contactno'];

$result= $pdo->prepare ("UPDATE client SET client_contact_number='$contact' WHERE client_id='$client'");
$result->execute;
}
?>

your syntax should be:

mysqli_query($connection, $sql_query)

you're missing the $connection object in your method.

PHP docs: http://php.net/manual/en/mysqli.query.php

*Original version of this question used procedural syntax - hence my answer.