Question

When I want to cast 1 to double, it does not work. When I cast 1.0 to double it works. Why?

I have the following code:

static void Main(string[] args)
{

    ArrayList liste1 = new ArrayList();
    liste1.Add(1);
    liste1.Add("Hallo");
    liste1.Add(2.5);

    double num = (double)liste1[0] + (double)liste1[2];

    Console.WriteLine(num);

    Console.ReadLine();
}

When I change liste1.Add(1); to liste1.Add(1.0); it works. Why does it work with 1.0 and not with 1?

It works too when I first cast liste1[0] to an int, and then to a double. Can you tell me why, please?

Thank you

Answer 1

ArrayList holds objects. If you add an int it gets “boxed” into an object and can only be “unboxed” back to int – not double.

MSDN: boxing & unboxing