How to fix "attempt to index ? (a number value)" ? LUA

The error occurs on line 112 when trying to use the goto() function.

I’m completely new to coding as of 4 days ago and am attempting to write a code that references a table for an argument to select a parameter for a function.

I want to enter changeD(a[4]) and have checkD() run until it returns a[4]. Instead i get the error code listed in the title.

My table is as follows

a = {}
a[1] = "north"
a[2] = "east"
a[3] = "south"
a[4] = "west"

I reference a table value as an argument in this function:

function changeD(arg)
local dir = 0
 repeat
  if checkD() == arg then
   print("Done")
   dir = 1
  else
  turn(1,1)
  end
 until dir == 1
end 

the checkD() function returns one of the table values. Therefore the changeD() function runs until the value returned by checkD() is the same as the table value specified in the argument.

I apologize if i’m using the wrong words to refer to the table stuff as I am still wet behind the ears when it comes to coding.

My full program is as follows. Sorry if its messy.

c = 0
a = {}
a[1] = "north"
a[2] = "east"
a[3] = "south"
a[4] = "west"
function fd(x)
 for i = 1 ,x do
  print("forward")
  turtle.dig()
  turtle.forward()
  end 
 end
 
function turn(y,x)
 if x == 1 then
  for i = 1 ,y do
  turtle.turnLeft()
  print("left")
  end
 elseif x == 2 then
  for i = 1 ,y do
  turtle.turnRight()
  print("right")
  end
 end
end
 
function checkD()
 local X, Y, Z = gps.locate()
 print(X)
 print(Y)
 print(Z)
turtle.forward()
 local x , y, z = gps.locate()
 print(x)
 print(y)
 print(z)
  c = 0
  result = false
  D = 0
repeat
 if c == 0 then 
  A = X
  B = x
 print(A.." "..B)
 else
  A = Z
  B = z
 print(A.." "..B)
 end
sleep(2)
 if A < B then
 g = 1
 elseif A > B then
 g = 2
 elseif A == B then
 c = 1
 end
print("compared values; g="..g)
if c == 0 then
 if g == 1 then
   D = a[2]
   result = true
 elseif g == 2 then
   D = a[4]
  result = true
 end
print("checked x")
print(D)
elseif not c == 0 then
 if g == 1 then
  D = a[3]
  result = true
 elseif g == 2 then
  D = a[1]
  result = true
 end
print("checked z")
end
print("Direction facing "..D)
 until result == true
 turtle.back()
 return D
end
 
function changeD(arg)
local dir = 0
 repeat
  if checkD() == arg then
   print("Done")
   dir = 1
  else
  turn(1,1)
  end
 until dir == 1
end 
local x = 0 
function goto(x,y,z)
local t = 0
local a = 0
local X, Y, Z = gps.locate()
  print(X)
  print(Y)
  print(Z)
 if X > x then
 t = X - x
 changeD(a[4])
 fd(t)
 elseif X < x then
 t = x - X
 changeD(a[2])
 fd(t)
 else
 print("cord is same")
 end
 
 if Z > z then
 t = Z - z
 change(a[1])
 fd(t)
 elseif Z < z then
 t = z - Z
 change(a[3])
 fd(t)
 else
 print("cord is same")
 end
 
 if Y > y then
  t = Y - y
  for i = 1,t do
   turtle.down()
  end
 elseif Y < y then
  t = y - Y
  for i = 1,t do
   turtle.up()
  end
 end
end

>Solution :

In goto, you declare local a = 0. This local a variable shadows the global a = {} variable. The local a variable is a number, so can’t be indexed.