Working lumberjack

term.clear()
term.setCursorPos(1,1)
print"Lumberjack 1.0"
print"Type 'exit' to exit program."
term.setCursorPos(1,4)
print"System: To start, please put dirt in slot 1, saplings in slot 2(Preferred not to be oak), and wood of the same type in slot 3."
print("System: When you do that, please enter the amount of trees to plant. Oh and remember, my fuel tank is at " .. turtle.getFuelLevel() .. ".")

write"You: "

local txt = io.read()

-- if exit then restart--
if txt == "exit" then
  os.reboot()
end
local dirt, sapling, wood = 1, 2, 3, 4
num = txt
tree = 0

print("System: Now planting " .. num .. " trees")

--Planting trees--
turtle.up()
turtle.down()
turtle.turnRight()
for i = 1, num do
  if turtle.detectDown() == false then
    turtle.select(dirt)
    turtle.placeDown()
  end
  turtle.back()
  turtle.select(sapling)
  turtle.place()
  turtle.turnLeft()
  turtle.forward()
  turtle.forward()
  turtle.forward()
  turtle.forward()
  turtle.turnRight()
  turtle.forward()
end

print("System: " .. num .. " trees were planted.")

--get back into position--
turtle.forward()
turtle.turnRight()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()

-- tree harvesting--
while true do
  sleep(30)
  for i = 1, num do
    turtle.turnRight()
    turtle.select(wood)
    if turtle.compare() == true then
      turtle.dig()
      turtle.forward()
      while turtle.detectUp() do
        turtle.digUp()
        turtle.up()
      end
      while not turtle.detectDown() do
        turtle.down()
      end
      turtle.back()
      turtle.select(sapling)
      turtle.place()
      tree = tree + 1
      print("System: " .. tree .. " trees were harvested.")
    end
    turtle.turnLeft()
    turtle.forward()
    turtle.forward()
    turtle.forward()
    turtle.forward()
  end
  turtle.turnRight()
  turtle.forward()
  turtle.forward()
  turtle.turnRight()
  turtle.forward()
  turtle.forward()
  turtle.forward()
  turtle.forward()
  print"System: Finished Checking trees."
end