This paper describes Macintosh features which can be used in writing interactive programs. A program written in Microsoft BASIC (version 2.0 interpreter) is described which is used to produce plots of electric field produced by two-dimensional arrangements of point charges. It demonstrates the use of pull-down menus, windows on the screen, the mouse, and buttons to make the program highly interactive. Actual screen graphics are included, but no program code is included. (JM)