attempt to compare nil with number stack traceback

[340919695]

i just started learning corona/lua yesterday, so i’m not exactly sure how to fix this. thanks for any and all help.

i finished the chapter one tutorial (the balloon one) and wanted the player to be able to collect stars to earn points. here is my code. i’m sorry there’s no tabs, i can’t seem to paste from sublime text to here with spaces.

if anyone knows how to fix that let me know.

[lua]

–balloon tap

– images

local sky = display.newImageRect(“myassets/skywatercolour.jpg”, 360, 570)

sky.x = display.contentCenterX

sky.y = display.contentCenterY

sky.id = “sky”

local balloon = display.newImageRect(“myassets/hotairballoon.png”, 300, 200)

balloon.x = display.contentCenterX

balloon.y = display.contentHeight - 170

balloon.id = “balloon”

local platform = display.newImageRect(“myassets/platform.png”, 230, 40)

platform.x = display.contentCenterX

platform.y = display.contentHeight

platform.id = “platform”

local pushes = 0

local score = display.newText("score: "…tostring(pushes), display.contentWidth -80, -10, native.systemFont, 25)

– physics

local physics = require(“physics”)

physics.start()

physics.addBody(platform, “static”, {bounce = 0.5})

physics.addBody(balloon, “dynamic”, {radius=76, bounce=0})

– walls

topWall = display.newRect(display.contentCenterX, -50, display.contentWidth, 2)

leftWall = display.newRect(0, 0, 2, display.contentHeight*2)

bottomWall = display.newRect(0, display.contentHeight*2, display.contentWidth*2, 2)

rightWall = display.newRect(display.contentWidth, 0, 2, display.contentHeight*2)

topWall.id = “topWall”

leftWall.id = “leftWall”

bottomWall.id = “bottomWall”

rightWall.id = “rightWall”

physics.addBody(topWall, “static”)

physics.addBody(leftWall, “static”)

physics.addBody(bottomWall, “static”)

physics.addBody(rightWall, “static”)

– functions

local function pushBalloon()

balloon:applyLinearImpulse(0, -1, balloon.x, balloon.y)

pushes = pushes + 1

score.text = "score: "…tostring(pushes)

end

local newStar

local stars = {}

local starAssets = {“myassets/star1.png”, “myassets/star2.png”, “myassets/star3.png”}

leftAndRight = {0, display.contentWidth}

local function spawnStar()

newStar = display.newImageRect(starAssets[math.random(#starAssets)], 20, 20)

table.insert(stars, newStar)

newStar.id = “star”…#stars

physics.addBody(newStar, “kinematic”, {bounce = 0})

newStar.x = leftAndRight[math.random(#leftAndRight)]

newStar.y = math.random(20, display.contentHeight - 200)

if (newStar.x == 0) then

newStar:setLinearVelocity(math.random(display.contentWidth/10, display.contentWidth-15), math.random(0, display.contentHeight/4))

elseif (newStar.x == display.contentWidth) then

newStar:setLinearVelocity(math.random(-display.contentWidth-15, -display.contentWidth/10), math.random(-display.contentHeight/4, 0))

end

newStar:applyTorque(math.random(-6, 6))

end

local function onCollision(self, event)

if (event.phase == “began”) then

local object = event.other.id

if string.match(object, “star”) then

pushes = pushes + 2

display.remove(event.other)

table.remove(stars, tonumber(string.sub(object, -1)))

elseif (object == “platform”) then

pushes = 0

end

score.text = "score: "…tostring(pushes)

end

end

– events

balloon.collision = onCollision

balloon:addEventListener(“collision”)

balloon:addEventListener(“tap”, pushBalloon)

– game loop

local function gameLoop()

if (#stars < 10) then

spawnStar()

end

for i = #stars, 1, -1 do

local currStar = stars[i]

– local xpos = tonumber(currStar.x)

– local ypos = tonumber(currStar.y)

– local width = tonumber(display.contentWidth)

– local height = tonumber(display.contentHeight)

print(type(currStar.x))

print(type(currStar.y))

print(type(display.contentWidth))

print(type(display.contentHeight))

if (currStar.x < -20) or (currStar.x > display.contentWidth + 20) or (currStar.y < -20) or (currStar.y > display.contentHeight + 20) then

display.remove(currStar)

table.remove(stars, i) 

end

end

end

loopTimer = timer.performWithDelay(500, gameLoop, 0)

[/lua]

i get the error Attempt to compare nil with number stack traceback on line 106 or

[lua] if (currStar.x < -20) or (currStar.x > display.contentWidth + 20) or (currStar.y < -20) or (currStar.y > display.contentHeight + 20) then [/lua]

as you can see, i checked the type of all the variables and they’re all numbers. i tried creating new variables hat are numbers and the same error occurred.

am i reading the error message wrong? is there a problem elsewhere? thank you for any help

[XeduR]

You are seeing that error simply because currStar does not exist.

You get that aforementioned error every time you try to access something inside a table when that table itself is nil. You can avoid crashes like this by always first checking if said table (or variable) exists, e.g.

if currStar and ((currStar.x \< -20) or (currStar.x \> display.contentWidth + 20) or (currStar.y \< -20) or (currStar.y \> display.contentHeight + 20)) then

Now, the reason why this is happening probably has something to do with how you remove the objects in your  onCollision function. Your gameLoop runs ever half a second, but while it is running, if one of those objects is removed while the loop is running, then the object won’t exist and the game will crash.

[340919695]

Oh, I see, thanks. Is there any work around for this? Would I have to check if the star exists on every step?

[XeduR]

I’m not sure what you mean. I already provided the code to prevent those crashes, so I am not sure what you are referring to.

By the way, out of curiosity. Did you personally choose the username “340919695” or is it some bug or something entirely different?

[340919695]

Oh… when I put it in, the crashes still occur with the same error.

I put in my school e-mail when I signed up so it just automatically chose that as my username. Definitely makes me look like a bot. I should probably change it.

[XeduR]

Did you copy it exactly as I put it and is it exactly that line that is crashing?

It first checks if  currStar  exists and is not false or nil, and if this condition is met, then it proceeds. The only way that line of code would crash is if currStar somehow existed and wasn’t false, nil OR a table. However, since you don’t assign any other values than tables to it, I don’t see how it could crash.

[340919695]

Oh, I fixed it! currStar remained a table but currStar.x and currStar.y were nil.

thank your so much for your help!!

final if statement was

[lua] if currStar and currStar.x and currStar.y and ((currStar.x < -20) or (currStar.x > display.contentWidth + 20) or (currStar.y < -20) or (currStar.y > display.contentHeight + 20)) then [/lua]

[XeduR]

While it is good that you got that sorted, just keep this in mind:

What you are doing now is basically just sweeping the problem under a rug. You should still go ahead and work on preventing the problem from ever occurring in the first place.

[XeduR]

You are seeing that error simply because currStar does not exist.

You get that aforementioned error every time you try to access something inside a table when that table itself is nil. You can avoid crashes like this by always first checking if said table (or variable) exists, e.g.

if currStar and ((currStar.x \< -20) or (currStar.x \> display.contentWidth + 20) or (currStar.y \< -20) or (currStar.y \> display.contentHeight + 20)) then

Now, the reason why this is happening probably has something to do with how you remove the objects in your  onCollision function. Your gameLoop runs ever half a second, but while it is running, if one of those objects is removed while the loop is running, then the object won’t exist and the game will crash.

[340919695]

Oh, I see, thanks. Is there any work around for this? Would I have to check if the star exists on every step?

[XeduR]

I’m not sure what you mean. I already provided the code to prevent those crashes, so I am not sure what you are referring to.

By the way, out of curiosity. Did you personally choose the username “340919695” or is it some bug or something entirely different?

[340919695]

Oh… when I put it in, the crashes still occur with the same error.

I put in my school e-mail when I signed up so it just automatically chose that as my username. Definitely makes me look like a bot. I should probably change it.

[XeduR]

Did you copy it exactly as I put it and is it exactly that line that is crashing?

It first checks if  currStar  exists and is not false or nil, and if this condition is met, then it proceeds. The only way that line of code would crash is if currStar somehow existed and wasn’t false, nil OR a table. However, since you don’t assign any other values than tables to it, I don’t see how it could crash.

[340919695]

Oh, I fixed it! currStar remained a table but currStar.x and currStar.y were nil.

thank your so much for your help!!

final if statement was

[lua] if currStar and currStar.x and currStar.y and ((currStar.x < -20) or (currStar.x > display.contentWidth + 20) or (currStar.y < -20) or (currStar.y > display.contentHeight + 20)) then [/lua]

[XeduR]

While it is good that you got that sorted, just keep this in mind:

What you are doing now is basically just sweeping the problem under a rug. You should still go ahead and work on preventing the problem from ever occurring in the first place.