Question

I’ve written a simple class, point, and I want to use it in a list.

In the list I have 3 points. If I print it:

for (int i = listOfPoint.Count -1; i >=0; i--)
{
    Console.WriteLine(listOfPoint[i].toString());
}

the output is:

(32, 10)
(33, 10)
(34, 10)

now, I want to do this:

for (int i = listOfPoint.Count -1; i > 0; i--)
{
    listOfPoint[i] = listOfPoint[i - 1];
}

after this – print:

(33, 10)
(34, 10)
(34, 10)

after this – I want to change the Y value of listOfPoint[0], so:

listOfPoint[0].Y = 11;

print the list again and the output is:

(33, 10)
(34, 11)
(34, 11)

Why isn’t the output:

(33, 10)
(34, 10)
(34, 11)

And how can I do it like this?

Answer 1

This happen because you have two element of the array referencing the same object. This is due to pointers.

Try to do this to avoid the problem:

for (int i = listOfPoint.Count -1; i > 0; i--)
{
    //Pass the value not the pointer
    listOfPoint[i] = new Point(listOfPoint[i-1].X, listOfPoint[i-1].Y);
}