PHP changing to mysqli. Is the mysqli_connection not global?

Yes, MySQLi is object oriented and you need to pass around the $db object to the functions that need a database connection. The procedural alternatives also require the $db object to work. This is for your own good, as implicit global connections (actually: global state in any form) are bad practice. That the mysql extension allowed implicit connections was not good to begin with.

Here's an option - create a static class purely to hold the mysqli object as a public static variable:

class DBi {    public static $conn;}DBi::$conn = new mysqli(HOST, USER, PASS, DB);

... in an include file, database helper or whatever.

Then wherever you want to make a mysqli call you do

DBi::$conn->query(...) 

Makes it as global as you could want. And you can easily start popping your own custom functions (methods) in there if you feel the need - DBi::custom_method()

This is kind of a refinement to the answer given at Converting mysql to mysqli - how to get superglobal connection object?

You need to set your $mysqli variable to be global if you need it in functions.

Something like this:

...function name (){          global $mysqli; ...