private static void Main(string[] args)
        {
            Product product1 = new Product(); //101

            product1.Id           = 1;
            product1.CategoryId   = 2;
            product1.ProductName  = "Masa";
            product1.UnitPrice    = 500;
            product1.UnitsInStock = 3;

            Product product2 = new Product
            {
                Id           = 2,
                CategoryId   = 5,
                UnitsInStock = 5,
                ProductName  = "Kalem",
                UnitPrice    = 35
            };

            //PascalCase   //camelCase
            //case sensitive
            ProductManager productManager = new ProductManager();

            productManager.Add(product1);
            Console.WriteLine(product1.ProductName);

            int numb = 100;

            productManager.DoThings(numb);
            Console.WriteLine(numb); //100

            productManager.Add2(product2);
            Console.WriteLine(product2.ProductName); //NewName

            //int,double,bool... value type
            //diziler,class, abstract class, interface ... reference type
            //ref out
        }