Attempt to compare nil with number?

I just typed a quarry program into an turtle on SSP and when I try to run it it lets me input the length, width, and height, but then it says "quarry:149: attempt to compare nil with number"

Here is the code around line 149:

volume = x*y*z
area = x*z

if maxslots > 15 then <———that's line 149
maxslots = 15
end
if Cdouble == 1 then
maxsize = maxsize/2
end

Any help would be great, I don't know much about code, but I've been able to debug it (mostly typos) up to this point

Does maxslots have a value prior to the if statement? Without seeing the rest of the code its a little difficult to help. About the advise I can give is for you to print maxslots prior to the if statement to see what its value is.

luanub, on 06 January 2013 - 07:01 PM said:

Does maxslots have a value prior to the if statement? Without seeing the rest of the code its a little difficult to help. About the advise I can give is for you to print maxslots prior to the if statement to see what its value is.

I'll have a go and say it doesn't because of the error, the only nil value there can be 'maxslots'

how do I define maxslots so that it still works with this part of the program? The full code is here: http://pastebin.com/u3CTvenK and the error in this code would be appearing on line 167

Well, can you tell us exactly what the variable is supposed to be doing?

–This is how many (theoretical) slots it will fill with cobble. e.g. 13 allows 13 slots for cobble (or other stack) and 2 slots for other things.
–Maximum here is 15 because 16 is for fuel
maxslots = 13

Okay, I'm lost. You clearly define maxslots at the beginning of the program, it's the first thing that gets done, and maxslots is global. You don't call any other programs that I can see (which could pose a problem), and you never redefine maxslots before the comparison.

Best I can suggest is to add the local keyword to the initial definition of maxslots just in case something else is accessing the global maxslots, but I can't see what.