Add item to array

Question

Point3d[] 3dpoints = new Point3d[] {

new Point3d(58, -4, 0),

new Point3d(60, -4, 0),

new Point3d(60, 98, 0),

new Point3d(58, 98, 0),

new Point3d(58, -4, 0)};

 

 

How to  add item to the above array