PHP code not updating database: while loop not executing UPDATE statement

I have a PHP script that is supposed to update a row in my database based on the ID of the user. However, the whileloop I’m using to execute the UPDATEstatement is not working. Here’s the relevant code:

require_once 'Connect DB.php';
$i=0;
while ($i=0) {
  if (isset($_POST["modifi"])) {
    $id_user = $_POST["modifi"];
    if(isset($_POST["send"])){
      $sql = 'update users set
            nom_user=''.$_POST["nom"].'',prenom_user=''.$_POST["prenom"].'',age_user=''.$_POST["age"].'',tel_user=''.$_POST["tel"].'' where id_user = ''."$id_user".''';
      $stmt = $con->exec($sql);
      $i=1;
    }
  }
}

When I submit the form with the send button, the UPDATE statement does not execute and the loop continues indefinitely. I suspect the while condition is the problem, but I’m not sure how to fix it.

Can anyone help me understand why this code is not working and how I can fix it? Thank you.