Error: Error: lua:1: attempt to index ? (a nil value)

function dig

    x = 0
    y = 0

    turtle.refuel()
    x = x+1
    while x == 1 do
        print("Refueled for the 1st time")
    while x == 2 do
        print("Refueled for the 2nd time")
    while x == 3 do
        print("Refueled for the 3rd time")
    while x == x>3 do
        print("Refueled for the "..x.."th time")
    end

    while turtle.detect() do
        turtle.dig()
        y = y+1
        turtle.forward()
    end

    while turtle.detect() == false do
        turtle.right()
        turtle.forward()
        turtle.right()
    end

    print("Your turtle has refueled "..x.." times!")
    print("Your turtle has dug "..y.." blocks!")
end



This is the other way i tried it: (I still got the same error, which one should i use to make it more efficient)


function dig

    x = 0
    y = 0

    turtle.refuel()
    x = x+1
    if x == 1 then print("Refueled for the 1st time")
    if x == 2 then print("Refueled for the 2nd time")
    if x == 3 then print("Refueled for the 3rd time")
    if x == x>3 then print("Refueled for the "..x.."th time")
    end

    while turtle.detect() do
        turtle.dig()
        y = y+1
        turtle.forward()
    end

    while turtle.detect() == false do
        turtle.right()
        turtle.forward()
        turtle.right()
    end

    print("Your turtle has refueled "..x.." times!")
    print("Your turtle has dug "..y.." blocks!")
end