mining semi advanced with variables?

turtle.select(2)
turtle.refuel()
local a = 0
-- a is for comparing length, b is for width, and c is determining right or left at the end, default is turn right at first --and switch.
local b = 0
local c = 0
local length = 60
local width = 60
local miners = 0
local height = 0
local fuellevel = turtle.getFuelLevel()

--check for file to save variables to
if not fs.exists("Adata", "w") then
  local file = io.open("Adata", "w")
  file:write()
  file:close()
end

if not fs.exists("Bdata", "w") then
  local file = io.open("Bdata", "w")
  file:write()
  file:close()
end

if not fs.exists("Cdata", "w") then
  local file = io.open("Cdata", "w")
  file:write()
  file:close()
end

local function saveDataA()
 local file = io.open("Adata", "w')
 file:write(a)
 file:close()
end


local function saveDataB()
 local file = io.open("Bdata", "w')
 file:write(b)
 file:close()
end

local function saveDataC()
 local file = io.open("Cdata", "w')
 file:write(c)
 file:close()
end

local file = io.open("Adata", "r") --open in read mode
a = file:read()
file:close()

local file = io.open("Bdata", "r") --open in read mode
b = file:read()
file:close()

local file = io.open("Cdata", "r") --open in read mode
c = file:read()
file:close()

repeat
repeat
  turtle.dig()
  if turtle.detect() == true then
  repeat
  turtle.dig()
  until turtle.detect() == false
  end
  turtle.forward()
  turtle.digDown()
  a = a + 1
  saveDataA()
  if turtle.getItemCount(16) ~= 0 then
  turtle.select(1)
  turtle.back()
  turtle.down()
  turtle.place()
  for i = 2,16 do
    turtle.select(i)
    turtle.drop()
  end
    turtle.up()
    turtle.forward()
    turtle.select(2)
  end
  until a == length

    a = 0
    if ( c == 0 ) then
      turtle.turnRight()
      turtle.dig()
      if turtle.detect() == true then
         repeat
         turtle.dig()
         until turtle.detect() == false
      end
      turtle.forward()
      turtle.digDown()
      turtle.turnRight()
      b = b + 1
      saveDataB()
    end
    if ( c == 1 ) then
      turtle.turnLeft()
      turtle.dig()
      if turtle.detect() == true then
        repeat
        turtle.dig()
        until turtle.detect() == false
      end
      turtle.forward()
      turtle.digDown()
      turtle.turnLeft()
      b = b + 1
    end
    if ( c == 1) then
      c = 0
      saveDataC()
    elseif ( c == 0) then
      c = 1
      saveDataC()
    else
    end
    turtle.refuel()
    fuellevel = turtle.getFuelLevel()
    print("number of runs "..b)
    print("fuel level " ..fuellevel)
    until b == width
a = 0
b = 0
c = 0
saveDataA()
saveDataB()
saveDataC()