代码已编译并且运行成功，但预期的输出是打印 "Sub" 未打印。这段代码有什么错误？

Code is compiled and run successfully but expected output is to print "Sub" is not getting printed. What is the error in this code?

这段代码有什么问题？

namespace ConsoleApplication1
{
public delegate void del();

class Program
{
    static void Main(string[] args)
    {
        del d = new del(add);
        d += sub;
    }

    public static void add()
    {
        Console.WriteLine("add");
    }

    public static void sub()
    {
        Console.WriteLine("Sub");
    }
  } 
}

您需要调用您的委托：

class Program
{
    static void Main(string[] args)
    {
        del d = new del(add);
        d += sub;

        d.Invoke();
    }

    public static void add()
    {
        Console.WriteLine("add");
    }

    public static void sub()
    {
        Console.WriteLine("Sub");
    }
  } 
}