Trouble with code to call custom fields into title

[mssbee]

Hello, I am working on this code and I wonder if I have made some basic mistakes as I am not very experienced at coding:

 

<?php

$mytitle=get_post_meta($post_,'Title', true);

$mycity=get_post_meta($post_,'City', true);

$mystate=get_post_meta($post_,'State', true);

$post_title=$mytitle.$mycity.$mystate;

$postdata = array( "ID" => $post_id, "post_title" => $post_title);

sanitize_post($postdata,"db");

wp_update_post($postdata);

?>

 

Thanks for any help anyone offers!