Variables Resetting When Using Parallel Function in Lua with ComputerCraft - function

Question

I am a beginner designing a Lua program in ComputerCraft (Minecraft) that asks the player for their name the first time they use it, and records it. For now, I want a program that detects if the variable firstnameis equal to nil and asks for the name if it is so. If the variable is not equal to nil, it says that you do not need to register. I currently have register()called only after pressing 5from the main menu.
The problem is that each time I assign a string to firstnameupon being prompted, firstnamereturns to nil when the main menu comes up. I even put print(firstname)at the end of the menu to test this.
I have assumed this is due to the parallel function that this all runs in. I run MainMenu() and Controls()in parallel so that I can listen for keyboard input and redstone input at the same time.
How can I keep both functions listening and the menu working, while preserving variables?
Here is the full code:
rednet.open("back") --Opens rednet on the back side of computer
local innerdooropen = false --Stuff to do with the airlock
local outerdooropen = false
function reset() --A handy function for screen reset
term.clear()
term.setCursorPos(1,1)
end
local function register() --This is the registration menu system
if firstname == nil then
print "Welcome to Obsidian Station!"
print "You must register before entering"
print "Please type your first name"
local firstname = read()
if firstname ~= "" then
print("Enter your last name")
local lastname = read()
print("You are now registered "..firstname.." "..lastname)
sleep(3)
rednet.broadcast(firstname.." "..lastname)
elseif firstname == "" then
print "You must register to enter"
shell.run("startup")
end
end
if firstname ~= nil then
print("Registration Not Needed")
sleep(2)
end
end
--Beginning of Section You Don't Have to Read
local function MainMenu()
while true do
term.clear()
term.setCursorPos(1, 1)
if innerdooropen == true then
rs.setOutput("left", false)
end
if outerdooropen == true then
rs.setOutput("right", false)
end
if innerdooropen == false then
rs.setOutput("left", true)
end
if outerdooropen == false then
rs.setOutput("right", true)
end
print "Safety Airlock Control"
print "~~~~~~~~~~~~~~~~~~~~~~"
print "[1] Open Outer Door"
print "[2] Open Inner Door"
print "[3] Close Both Doors"
print ""
print "[4] Open Both Doors - WARNING! DANGEROUS!"
print ""
print "[5] Register"
print(firstname)
input = read()
if input == "2" then
print "Inner Door Open"
outerdooropen = false
sleep "1"
innerdooropen = true
end
if input == "1" then
print "Outer Door Open"
innerdooropen = false
sleep "1"
outerdooropen = true
end
if input == "3" then
print "Both Doors Closed"
innerdooropen = false
outerdooropen = false
end
if input == "5" then
reset()
register()
end
if input == "6" then
print("firstname: "..firstname)
sleep(3)
end
if input == "4" then
term.clear()
term.setCursorPos(1, 1)
print "CONFIRM BOTH DOORS OPEN? [y] [n]"
input = read()
if input == "y" then
print "OPENING AIRLOCK DOORS IN"
sleep "1"
print "10"
sleep "1"
print "9"
sleep "1"
print "8"
sleep "1"
print "7"
sleep "1"
print "6"
sleep "1"
print "5"
sleep "1"
print "4"
sleep "1"
print "3"
sleep "1"
print "2"
sleep "1"
print "1"
sleep "1"
innerdooropen = true
outerdooropen = true
print "DOORS OPEN"
sleep "1"
end
elseif input == "n" then
term.clear()
term.setCursorPos(1, 1)
shell.run("startup")
end
end
end
--end of section you don't have to read
local function Controls()
while true do
local e = os.pullEvent()
if e == "redstone" and rs.getInput("bottom") then
redstone.setOutput ("left", true)
sleep "1"
redstone.setOutput ("right", false)
innerdooropen = true
outerdooropen = false
end
end
end
while true do
parallel.waitForAll(MainMenu,Controls)
end

Answer 1

Initialize firstname outside of the parallel. Put local firstname up at the top of your code, and change local firstname = read() to just firstname = read(), and do the same for last name.
You are creating the variable after you check whether or not it is nil, which is why it always returns nil. Similarly, when the function ends, firstname no longer exists, since it is called and created inside of the function. So it will always return nil.
The top of your code should look like so
rednet.open("back") --Opens rednet on the back side of computer
local innerdooropen = false --Stuff to do with the airlock
local outerdooropen = false
local firstname = ""
local lastname = ""
And the other section should be as follows:
if firstname == nil then
print "Welcome to Obsidian Station!"
print "You must register before entering"
print "Please type your first name"
firstname = read()
if firstname ~= "" then
print("Enter your last name")
lastname = read()
print("You are now registered "..firstname.." "..lastname)
sleep(3)

Answer 2

You should initialize firstname before you check if it is equal to nil.
local firstname = nil; --Move this up here so that you can access it elsewhere.
local lastname = nil; --This is also needed out here.
local function register() --This is the registration menu system
if firstname == nil then
print "Welcome to Obsidian Station!"
print "You must register before entering"
print "Please type your first name"
firstname = read() --Change this to just setting firstname to the read name.
if firstname ~= "" then
print("Enter your last name")
lastname = read()
print("You are now registered "..firstname.." "..lastname)
sleep(3)
rednet.broadcast(firstname.." "..lastname)
elseif firstname == "" then
print "You must register to enter"
shell.run("startup")
end
end
if firstname ~= nil then --Now this will not error as well.
print("Registration Not Needed")
sleep(2)
end
end
This allows for firstname to be accessed elsewhere and not just within that first if statement. You were checking if an uninitialized variable was equal to nil or not.
EDIT: Saw purxiz's answer and realized that you also probably want lastname to be outside of the loop. I fixed it in my code above now.