private void Shopping(string buying) { string[] buyingArr = buying .Split(" ", StringSplitOptions.RemoveEmptyEntries).ToArray(); string name = buyingArr[0].Trim(); string product = buyingArr[1].Trim(); if (name == "" || product == "") { Console.WriteLine("Name cannot be empty"); throw new ArgumentException(); } Product productToBuy = products.Find(x => x.Name == product); Person person = people.Find(x => x.Name == name); person.BuyingProduct(productToBuy); }