Use blocks from the More Blocks tab, the Control tab, the Looks tab, and the Sensing tab to make a program that moves Sidney from start to end. Portals are set up in such a way that the portal entrance will randomly send Sidney to a portal exit. The "repeat until" block allows Sidney to repeated pass through a portal entrance until it teleports to the correct portal exit.
Based on a design from MyCS_Student and the work of the students at Harvey Mudd College.
