as is not allowed as name for a variable, because it´s a keywors used in C#. you´d better be off by use another name, e.g. ÀddStock`.
If you really need/want to use that name use the
@ in front:
AddStock @as = new AddStock();
But then you´d have to add that operator whenever you´re using that variable, e.g. the following would cause a compiler-error:
whereas this won´t: