Udig - Mining Turtle

-- change mx for width, my for length and mz for height, the turtle will dig down and to the right
mx = 50
my = 50
mz = 10
-- Dont change anything bellow this line

x = 0
y = 0
z = 0
cx = 0
cy = 0
cz = 0

posy = 0
posx = 0

function f()
if turtle.forward() == false then
  repeat
  turtle.dig()
  sleep(0.25)
  until turtle.forward() == true
end
end

function d()
if turtle.down() == false then
  repeat
  turtle.digDown()
  sleep(0.25)
  until turtle.down() == true
end
end

function u()
if turtle.up() == false then
  repeat
  turtle.digUp()
  sleep(0.25)
  until turtle.up() == true
end
end

function check()
for i = 1,8 do
  if turtle.getItemCount(i) == 0 then
   return true
  end
end
end

function dropall()
for dropSlot = 1,9 do
  turtle.select(dropSlot)
  turtle.drop()
end
turtle.select(1)
turtle.turnRight()
turtle.turnRight()
end

function down()
while cz < mz do
  d()
  cz = cz+1
end
end

function up()
while cz > z do
  u()
  cz = cz-1
end
end

function bdig()
if cz == z and cx == x then
  goback()
  dropall()
else
  up()
  goback()
  dropall()
end
end

function goback()
posy = cy
posx = cx + 1
print("y - ",posy)
print("x - ",posx)
turtle.turnLeft()
while cx > x do
  f()
  cx = cx - 1
end
turtle.turnLeft()
while cy > y do
  f()
  cy = cy - 1
end
end

function udig()
while check() and cy < my do
  turtle.digUp()
  down()
  up()
  f()
  cy = cy+1
end
bdig()
end

while true do
if posx == x then
  while cy < posy do
   f()
   cy = cy + 1
  end
  udig()
elseif posx < mx and posy == my then
  turtle.turnRight()
  while cx < posx do
   f()
   cx = cx + 1
  end
  turtle.turnLeft()
  udig()
elseif posx < mx and posy ~= my then
  turtle.turnRight()
  while cx < posx - 1 do
   f()
   cx = cx + 1
  end
  turtle.turnLeft()
  while cy < posy do
   f()
   cy = cy + 1
  end
  udig()
elseif posy == my and posx == mx then
  print("Complete")
  break
end
end