Gps Not Working

I have building a mining program but the gps is reporting nil even though the debug reports a value.

a = 0
print("Are there GPS satellites in the sky?")
input = read()
if input == "No" then
  error("There must be a GPS system in place to use this program!")
end
if input == "Yes" then
  local x, y, z = gps.locate(2,true)
  y = by --Backup for y
  print(y) --No value 
  if y == nil then
    error("Nope, still lost :(/>/>")
    end
  for i = 1,tonumber(y) do --It says that y is not a number 
    turtle.digDown()
    turtle.down()
    repeat
      if turtle.detect() then
        turtle.dig()
        end
      turtle.turnLeft()
      a = a + 1
     until a > 4
    end
  while by ~= 1 do
    turtle.up()
    by = by - 1
    end
  turtle.select(2)
  turtle.placeDown()
end

Also, could I have some feedback on the code, please?

Before this bit of code runs, what is by set to?
If you never set by, then by is nil. Then you do "y = by" so y is also nil. Then you error because y is nil.

cmckain14, on 26 September 2013 - 12:52 AM said:

y = by --Backup for y
print(y) --No value 
if y == nil then
  error("Nope, still lost :(/>/>/>/>")
end

One small tidbit of feedback. You have two if statements to check one instance of user input. It is probably better to use 1 if block to check the one input.

input = read()
if input == "no" then
  error("There must be a GPS system in place to use this program!")
elseif input == "yes" then -- or just simply else
  --insert rest of code here
end

In this bit of code its not really a big deal but in the larger scheme of things its a good habit to get into.

Luanub, on 26 September 2013 - 03:40 AM said:

One small tidbit of feedback. You have two if statements to check one instance of user input. It is probably better to use 1 if block to check the one input.

input = read()
if input == "no" then
  error("There must be a GPS system in place to use this program!")
elseif input == "yes" then -- or just simply else
  --insert rest of code here
end

In this bit of code its not really a big deal but in the larger scheme of things its a good habit to get into.

More importantly though, what happens if they type "banana"?

immibis, on 26 September 2013 - 04:17 AM said:

Luanub, on 26 September 2013 - 03:40 AM said:

One small tidbit of feedback. You have two if statements to check one instance of user input. It is probably better to use 1 if block to check the one input.

input = read()
if input == "no" then
  error("There must be a GPS system in place to use this program!")
elseif input == "yes" then -- or just simply else
  --insert rest of code here
end

In this bit of code its not really a big deal but in the larger scheme of things its a good habit to get into.

More importantly though, what happens if they type "banana"?

Or No/Yes instead of no/yes. Definitely could use some extra error checking/prevention.

It could look something like…

local input = string.lower(read()) --make the var local and convert to lower case
if input == "no" then
  --error
elseif input == "yes" then
--run the code
else
   error("Invalid answer")
end

There are also other ways to accomplish this but hopefully that shows the general idea.

immibis, on 26 September 2013 - 03:01 AM said:

Before this bit of code runs, what is by set to?
If you never set by, then by is nil. Then you do "y = by" so y is also nil. Then you error because y is nil.

cmckain14, on 26 September 2013 - 12:52 AM said:

y = by --Backup for y
print(y) --No value 
if y == nil then
  error("Nope, still lost :(/>/>/>/>/>")
end

But why is y nil when the GPS should define it?

by = y == y cord
y = by == nil

your backup is deleting the y cord.

smal derp

cmckain14, on 26 September 2013 - 09:54 AM said:

immibis, on 26 September 2013 - 03:01 AM said:

Before this bit of code runs, what is by set to?
If you never set by, then by is nil. Then you do "y = by" so y is also nil. Then you error because y is nil.

cmckain14, on 26 September 2013 - 12:52 AM said:

y = by --Backup for y
print(y) --No value 
if y == nil then
  error("Nope, still lost :(/>/>/>/>/>/>/>/>")
end

But why is y nil when the GPS should define it?

Because you made it nil after that.
"by" is nil.
"y = by" sets "y" to whatever "by" is.
Therefore, "y = by" sets "y" to nil (in this program).