Why can't I modify the array in the first function? [duplicate]

I want to modify the array in the first function using the second function but it doesn't return the result where it should(first Function).

    function first(){
    $results = [
        'programs' => [],
        'events' => [],
    ];
    second('program', $results);
    print_r($results); // Don't get results here
}

function second($type,$arr){
    $type .= 's';
    if(array_key_exists($type,$arr)){
        array_push($arr[$type],'title');
    }
    print_r($arr); // Get results here
}
first();