获取laravel中生成的发票号

Question

I'm trying to generate an invoice number, but I'm getting A non-numeric value encountered. I think I'm missing something but I'm not sure what it is.

Here is the invoiceNumber() code in my helpers.php

function invoiceNumber()
{
    $orders = App\Order::all();

    if($orders->isEmpty())
    {
        $invoice = 'arm0001';
        return $invoice;
    }

    foreach($orders as $order)
    {
        $latest = App\Order::latest()->first();

        if($latest->invoice_number == true)
        {
            $invoice = 'arm'.$latest->invoice_number+1;
            return $invoice;
        }
    }
}

and this is where I'm trying to get it to be taken

public function deliveryConfirmation()
{
    $menus_child = Menu::where('menu_id', 0)->with('menusP')->get();
    $contacts = Contact::all();

    if(!Session::has('cart'))
    {
        return view('public.shopping-cart', compact('menus_child', 'contacts'));
    }

    $oldCart = Session::get('cart');
    $cart = new Cart($oldCart);

    $invoice_number = invoiceNumber();
    dd($invoice_number);

    return view('public.delivery-confirmation', ['products' => $cart->items, 'totalPrice' => $cart->totalPrice, 'menus_child' => $menus_child, 'contacts' => $contacts, 'invoice_number' => $invoice_number]);
}

I would really like to keep the 'ARM' in the database as well

Answer 1

So after seeing everyone's answer and from my understanding, it looked like everyone was separating the integer from the string to get it to work and it got me thinking about doing a preg_replace(). so I've adjusted my code to look like this

function invoiceNumber()
{
    $latest = App\Order::latest()->first();

    if (! $latest) {
        return 'arm0001';
    }

    $string = preg_replace("/[^0-9\.]/", '', $latest->invoice_number);

    return 'arm' . sprintf('%04d', $string+1);
}