Maybe something like..
PHP Code:
if (isset($messagesToUpdate) && $messagesToUpdate) {
// Update Selected Messages.
$parmcount = count($messagesToUpdate);
$inclause = implode(',', array_fill(0, $parmcount, '?')); // = ?,?,?,?
// Build query.
$q1 = "UPDATE private_msg_recipient
SET read_on = NULL,
updated_on = NOW()
WHERE member_id_to = ?
AND message_id IN (%s)";
$preparesql = sprintf($q1, $inclause);
// Prepare statement.
$stmt1 = mysqli_prepare($dbc, $preparesql);
array_unshift($messagesToUpdate, $sessMemberID);
$type = 'i' . str_repeat('i', $parmcount);
// Bind variables to query.
call_user_func_array('mysqli_stmt_bind_param',
array_merge(array($stmt1, $type), $messagesToUpdate));
// Execute query.
mysqli_stmt_execute($stmt1);
// Verify Update.
if (mysqli_stmt_affected_rows($stmt1) == 1) {
// Update Succeeded.
} else {
// Update Failed.
}