Editor's Note: This LISP file was updated in August 2011. The update does not affect the operation of the commands themselves; the only change is that using Undo after the commands now works as expected.
Kent Cooper submits two complementary functions in this LISP file. The first one converts circle entities to polylines in AutoCAD; the other converts polylines to circles. (Of course the second function can only convert polylines that can be represented by a circle, such as those created with the Donut command.) Start by loading the LISP file, then type in C2P to convert circles to polylines, or P2C to convert polylines to circles. Existing properties such as color, linetype, and lineweight are maintained, and both commands work in any UCS. Be sure to read the comments in this well-documented LISP file, which contain more details on the operation and limitations of these functions.