bad argument #1 to 'pairs' (table expected, got nil) - lua

Question

So I'm trying to program a space invaders like game in lua using löve2d, the first wave of enemies runs smoothly but once i try adding another wave to the levelctrl table i get this error: bad argument #1 to 'pairs' (table expected, got nil) on line 235 (even when i populate a second table)
function love.load()
hero = {}
hero.x = 400 - 16
hero.y = 450
hero.speedx = 300
hero.speedy = 50
hero.shots = {}
bgx = 0
bgs = .25
fleet1 = {}
f1x = 0
f1f = 0
lost = 0
score = 0
game = 0
menu = 1
startup = 1
--Images
bg = love.graphics.newImage("img/space.png")
bullet = love.graphics.newImage("img/shot.png")
player = love.graphics.newImage("img/player.png")
trail = love.graphics.newImage("img/trail.png")
ship1 = love.graphics.newImage("img/enemy1.png")
looser = love.graphics.newImage("img/looser.png")
boomp1 = love.graphics.newImage("img/boomp1.png")
boomp2 = love.graphics.newImage("img/boomp2.png")
boomp3 = love.graphics.newImage("img/boomp3.png")
boomp4 = love.graphics.newImage("img/boomp4.png")
boom1 = love.graphics.newImage("img/boom1.png")
boom2 = love.graphics.newImage("img/boom2.png")
boom3 = love.graphics.newImage("img/boom3.png")
boom4 = love.graphics.newImage("img/boom4.png")
winner = love.graphics.newImage("img/winner.png")
title = love.graphics.newImage("img/title.png")
message = love.graphics.newImage("img/message.png")
restart = love.graphics.newImage("img/restart.png")
icon = love.graphics.newImage("img/icon.gif")
boomtimer=0
isdead=0
boom={}
bgs = .25
bgx = 0
menublink = 0
menuf = 0
end
function love.update(dt)
if bgx < 600 then
bgx = bgx + bgs
else
bgx = -599
end
if bgs > .30 then
bgs = bgs - 2*dt
end
if menublink < 48 and menuf==0 then
menublink = menublink + 1
else
menuf=1
menublink = menublink -1
if menublink == 0 then
menuf=0
end
end
if menu == 1 then
hero = {}
hero.x = 400 - 16
hero.y = 450
hero.speedx = 300
hero.speedy = 50
hero.shots = {}
f1x = 0
f1f = 0
lost = 0
score = 0
boomtimer=0
isdead=0
won=0
boom={}
fleet1 = {}
for i=0,7 do
enemy = {}
enemy.width = 32
enemy.height = 16
enemy.img = ship1
enemy.x = i * (enemy.width + 64) + 48
if i<4 then
if i % 2 == 0 then
enemy.y = 0 - enemy.height
else
enemy.y = -16 - enemy.height
end
else
if i % 2 == 0 then
enemy.y = -16 - enemy.height
else
enemy.y = 0 - enemy.height
end
end
table.insert(fleet1, enemy)
end
boss = {}
level = 1
levelctrl = {}
table.insert(levelctrl, fleet1)
if love.keyboard.isDown(" ") then
menu = 0
game = 1
end
elseif game == 1 then
if isdead==0 then
if love.keyboard.isDown("left") then
if hero.x > 0 then
hero.x = hero.x - hero.speedx*dt
end
elseif love.keyboard.isDown("right") then
if hero.x < 800-32 then
hero.x = hero.x + hero.speedx*dt
end
end
if love.keyboard.isDown("up") then
if hero.y > 300 then
hero.y = hero.y - hero.speedy*dt
up=1
else
up=0
end
if bgs < 4 then
bgs = bgs + 5*dt
end
elseif love.keyboard.isDown("down") then
if hero.y < 600-64 then
hero.y = hero.y + hero.speedy*2*dt
end
else
up=0
end
end
for i,v in ipairs(hero.shots) do
v.y = v.y - dt * 300
end
if won == 0 then
local remShot = {}
local remEnemy = {}
for i,v in ipairs(hero.shots) do
if v.y < 0 then
table.insert(remShot, i)
end
for ii,vv in ipairs(levelctrl[1]) do
if CheckCollision(v.x,v.y,32,32,vv.x,vv.y,vv.width,vv.height) then
x = {}
x.x = vv.x
x.y = vv.y
x.t = 0
table.insert(boom, x)
table.insert(remEnemy, ii)
table.insert(remShot, i)
end
end
end
for i,v in ipairs(levelctrl[1]) do
if CheckCollision(hero.x,hero.y,32,64,v.x,v.y,v.width,v.height) then
lost = 1
end
end
for i,v in ipairs(remShot) do
table.remove(hero.shots, v)
end
for i,v in ipairs(remEnemy) do
table.remove(levelctrl[1], v)
score = score + 1
end
if level == 1 then
for i,v in ipairs(levelctrl[1]) do
v.y = v.y + dt * 12
if v.y > 512 then
lost = 1
end
if v.x>0 and v.x < 768 then
if f1f == 0 then
if f1x<3 then
f1x = f1x + 1 * dt
v.x = v.x + 1
else
f1f = 1
end
else
if f1x>-3 then
f1x = f1x - 1 * dt
v.x = v.x - 1
else
f1f = 0
end
end
end
end
end
end
if empty(levelctrl[1]) == true and won == 0 then
level = level + 1
table.remove(levelctrl, 1)
if remEnemy ~= nil then
for k in pairs (remEnemy) do
remEnemy[k] = nil
end
end
end
if won == 1 and love.keyboard.isDown("return") then
menu = 1
game = 0
elseif lost == 1 and love.keyboard.isDown("return") then
menu = 1
game = 0
end
end
end
function love.draw()
love.graphics.setIcon(icon)
love.graphics.setColor(255,255,255,255)
love.graphics.draw(bg, 0, bgx)
love.graphics.draw(bg, 0, bgx-1199)
if menu == 1 then
love.graphics.draw(title)
if menuf == 1 then
love.graphics.draw(message)
end
elseif game == 1 then
for i,v in ipairs(hero.shots) do
love.graphics.draw(bullet, v.x, v.y)
end
if up==1 then
love.graphics.draw(trail, hero.x, hero.y)
end
for i,v in ipairs(levelctrl[1]) do
love.graphics.draw(v.img, v.x, v.y)
end
if lost == 0 then
love.graphics.draw(player, hero.x, hero.y)
else
isdead=1
if boomtimer<8 then
love.graphics.draw(boomp1, hero.x-16, hero.y)
boomtimer = boomtimer + 1
elseif boomtimer<16 then
love.graphics.draw(boomp2, hero.x-16, hero.y)
boomtimer = boomtimer + 1
elseif boomtimer<24 then
love.graphics.draw(boomp3, hero.x-16, hero.y)
boomtimer = boomtimer + 1
elseif boomtimer<32 then
love.graphics.draw(boomp4, hero.x-16, hero.y)
boomtimer = boomtimer + 1
else
love.graphics.draw(looser)
if menuf == 1 then
love.graphics.draw(restart, 0, 20)
end
end
end
for i,v in ipairs(boom) do
if v.t<8 then
love.graphics.draw(boom1, v.x, v.y-8)
v.t = v.t + 1
elseif v.t<16 then
love.graphics.draw(boom2, v.x, v.y-8)
v.t = v.t + 1
elseif v.t<24 then
love.graphics.draw(boom3, v.x, v.y-8)
v.t = v.t + 1
elseif v.t<32 then
love.graphics.draw(boom4, v.x, v.y-8)
v.t = v.t + 1
else
table.remove(boom, i)
end
end
if won == 0 then
if empty(levelctrl) then
won = 1
end
end
if won == 1 then
love.graphics.draw(winner)
if menuf == 1 then
love.graphics.draw(restart, 0, 20)
end
end
end
end
function shoot()
local shot = {}
shot.x = hero.x
shot.y = hero.y - 4
table.insert(hero.shots, shot)
end
function CheckCollision(ax1,ay1,aw,ah, bx1,by1,bw,bh)
local ax2 = ax1 + aw
local ay2 = ay1 + ah
local bx2 = bx1 + bw
local by2 = by1 + bh
return ax1 < bx2 and ax2 > bx1 and ay1 < by2 and ay2 > by1
end
function love.keyreleased(key)
if isdead==0 then
if (key == " ") then
shoot()
end
end
end
function empty(self)
for _, _ in pairs(self) do
return false
end
return true
end
that's all the code and more specifically i get a problem with this:
for i,v in ipairs(levelctrl[1]) do
love.graphics.draw(v.img, v.x, v.y)
end
levelctrl initially has 2 tables inside so after i remove the first one to bump the second one down, I recieve the bad argument error

Answer 1

The problem seems to be around line 200:
if empty(levelctrl[1]) == true and won == 0 then
level = level + 1
table.remove(levelctrl, 1)
Here you remove the table from levelctrl when it's empty and increase the level. Since the table is empty already, can't you just re-use it instead of removing it (causing crashes on next rendering)? Removing the table.remove call should help.

Answer 2

I see
levelctrl = {}
table.insert(levelctrl, fleet1)
So levelctrl = {fleet1}
and some time later when you win,
if empty(levelctrl[1]) == true and won == 0 then
level = level + 1
table.remove(levelctrl, 1)
So levelctrl = {}
won is still 0, and game is still 1.
Then in your draw function
for i,v in ipairs(levelctrl[1]) do
love.graphics.draw(v.img, v.x, v.y)
end
At this point levelctrl = {} and levelctrl[1] = nil.
One solution would be to surround that bit of your draw function with
if not empty(levelctrl)
Also if you were trying to add fleet1 to levelctrl multiple times,
levelctrl = {}
table.insert(levelctrl, fleet1)
table.insert(levelctrl, fleet1)
table.insert(levelctrl, fleet1)
Then levelctrl would have three instances of the same table, and removing something from levelctrl[1] would remove it from fleet1 => all of the levels become empty at the same time.