MainProgram:
  gosub DrawEnvironment
  for i=1 to 10  // perform 10 iterations
    gosub InitRobot
    gosub GoThroughDoor
  next
end

DrawEnvironment:
  // draw walls
  LineWidth 2
  Rectangle 200,290,350,310,black,gray
  Rectangle 420,290,600,310,black,gray
Return

InitRobot:
  rLocate 225+random(11),345+random(11),-5+random(11)
  rInvisible GREEN
  rPen DOWN
  rSlip 10  // %error
Return

// Program for Servo Article on programming sensors (Nov. 2016)
// Download RobotBASIC to run this program (RobotBASIC.org) 
// experiment with the modifications discussed in the article

GoThroughDoor:
  gosub FindDoor
  gosub PassThrough
Return

FindDoor:
  rTurn 90
  dist = rRange(-90)
  // follow wall to doorway
  repeat
    if rRange(-90)<dist then rTurn  1
    if rRange(-90)>dist then rTurn -1
    rForward 1
  until rRange(-80)>10+dist
  rForward 60 
Return

PassThrough:     
  rTurn -90
  while (rFeel()&17)!=17
    rForward 1 
    if rFeel()&8 then rTurn 1
    if rFeel()&2 then rTurn -1 
  wend  
  rForward 50
  // draw a circle to show where the robot stops
  // only needed when multiple iterations are used
  rGPS x,y
  linewidth 3
  setcolor green
  circle x-18,y-18,x+18,y+18
Return