Index expected: got nil BUT ITS DECLARED

I have been working on a program that keeps a big reactor multiblock in equilibrium by managing the levels of input and output fluid and trying to optimize based on temperature. For this, I am using a few arrays that let me better keep track of average values that I get from some of the sensors. I have written this snippet of my code to initialize the 10 elements of 2 arrays to all 0 so that it doesnt return nil whenever I average it for the first few ticks. I attempted to initialize the values below as described below but I get an error on line '2' ( as relative to how it is pasted) that says "<programname>:<2>: index expected, got nil. I assumed that putting index = 1 would initialize the variable 'index' to 1 and so it should not be nil. But the interpreter says that it is. What am I doing wrong and how can I fix it?

for index=1,10,1 do
tempArray[index] = 0
fluidArray[index] = 0
end

Did you declare the tempArray table, though?

I am unsure of what a table is, but I did try declaring the array with a different method above that loop and it still didnt work

tempArray[10] = {0,0,0,0,0,0,0,0,0,0}
fluidArray[10] = {0,0,0,0,0,0,0,0,0,0}

It should be:

local tempArray = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}

Ok that makes sense, now how would I declare it in a loop?

You'd use your original code, but before the loop, you'd declare the tables:

local tempArray = {}
local fluidArray = {}

Just to make it clear: there are no arrays in Lua. There are only tables. Make sure to read about them here.

… which, while true, is pretty ironic when you consider that the table API only contains functions that're relevant to arrays.