Function connections with mysqli

================ File connection.php ====================
<?php

function connectionDB() {
    global $mysqli;

    $mysqli = mysqli_connect( "localhost", "root", "", "mahasiswa" );

    if ( mysqli_connect_errno() ) {
        printf( "Connect failed: %s\n", mysqli_connect_error() ;
        exit();

    }
}
?>

================== Other files =====================
<?php
include "connection.php";
connectionDB();

$sql = "INSERT INTO Bla bla... ";

//etc ..
?>