' Problem: You have 100 doors in a row that are all initially closed. You make
' 100 passes by the doors. The first time through, you visit every door and
' toggle the door (if the door is closed, you open it; if it is open, you
' close it). The second time you only visit every 2nd door (door #2, #4, #6,
' ...). The third time, every 3rd door (door #3, #6, #9, ...), etc, until you
' only visit the 100th door.

' Question: What state are the doors in after the last pass? Which are open,
' which are closed? 

FOR p = 1 TO 100
  FOR d = p TO 100 STEP p
    @(d) = @(d) = 0
  NEXT d
NEXT p

FOR d= 1 TO 100
  IF @(d) PRINT "Door ";d;" is open"
NEXT d