I cannot get my last index to be the first index C#

Question

I have an array list that I'm copying from another method I have made but I just need to reverse it and swap the last value to be the first value. I have thought about doing it this way but for some reason the Prepend is not working at all. RemoveAt is working however. is there an alternative to what I am doing that can get this work?

List<double> pointy = new List<double>
            {
                0,
                FrameHeight-24,
                FrameHeight-24+2,
                FrameHeight-24+2,
                FrameHeight-24+2-3,
                FrameHeight-24+2-3,
                FrameHeight-24+2-3+1,
                FrameHeight-24+2-3+1+2,
                FrameHeight-24+2-3+1+2,
                FrameHeight-24+2-3+1,
                FrameHeight-24+2-3,
                FrameHeight-24+2-3,
                FrameHeight-24+2,
                FrameHeight-24+2,
                FrameHeight-24+2+2,
                FrameHeight,
                FrameHeight,
                0,
                0
            };

            pointy.Prepend(pointy[(pointy.Count) - 1]).ToList();
            pointy.RemoveAt((pointy.Count)-1);
            pointy.Reverse();

Answer 1

If you study the docs, as others link to, you'll see that Prepend() and ToList() don't work exactly like you think, In particular, there is absolutely no point in calling .ToList() without using the returned value.

Instead, there already exists a method on the List class which does exactly what you want:

pointy.Insert(0, pointy[pointy.Count - 1]);

or

pointy.Insert(0, pointy.Last());

Full method being

public void ChangeList(List<double> arrayList)
        {
            arrayList.Insert(0, arrayList.Last());
            arrayList.RemoveAt(arrayList.Count - 1);
            arrayList.Reverse();
        }