string order_stream = "B123,C234,A345,C15,B177,G3003,C235,B179";
string[] order_ids = order_stream.Split(',');
Array.Sort(order_ids);

foreach (var order_id in order_ids) {
    int id_length = order_id.Length;
    if (id_length == 4) {
        Console.WriteLine(order_id);
    } else {
        int remainder = 8 - id_length;
        string spaces = new String(' ', remainder);
        Console.WriteLine(order_id + spaces + "- Error");
    }
}