Can't access array value using variables

Question

i am using the p5js libary and ran into a problem that i have never had before. I have a function called neighbors with the constructor neighbors(x, y). I call that function multiple times each loop (2500 times). If i use this code:

if(x < 50){
    if(spots[1][1]){
        neighborCount++;
    }
}

nothing goes wrong. As soon as i replace the code with this:

if(x < 50){
    if(spots[parseInt(x+1)][1]){
        neighborCount = 3;
    }
}

I get an error in the console:

TypeError: spots[(x + 1)] is undefined

I tried using

spots[parseInt(x+1)][1]

but that only changed the error to

TypeError: spots[parseInt(...)] is undefined

I hope i explained my problem well enough and you can understand it. If i forgot something please tell me i will add it as soon as possible.

Thanks in advance

FritzFurtz

What is x? And why do you use parseInt on what appears to be a number? — Bergi
– Bergi, Commented Mar 23, 2017 at 14:34
x is a number between 0 and 49. Oh i think i just found my mistake. I check if x < 50 but it is always smaller 50. Let me check that now. Oh yes. Array 0 indexing... Thanks for asking questions, that always help :) — FritzFurtz
– FritzFurtz, Commented Mar 23, 2017 at 14:37

FritzFurtz · Accepted Answer · 2017-03-23 14:38:35Z

1

I did a classic mistake: 0 indexing in arrays. The if(x < 50) was supposed to check if it is undefinded, because the array size is 50. But i forgot that the last value is indexed 49 so i have to check if(x < 49). Thank you guys for always answering fast!

answered Mar 23, 2017 at 14:38

FritzFurtz

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2 Comments

Maurice Perry Over a year ago

I don't get it.

FritzFurtz Over a year ago

I access x+1. If i do that i have to check that x + 1 is not undefined and for that i made a if(x < 50), because the array size is 50. But since arrays are 0 indexed, i had to make a if(x < 49) so that x + 1 can be max. 49

remborg · Accepted Answer · 2017-03-23 14:33:41Z

0

try with this

if(x < 50){
    if(spots[parseInt(x,10)+1][1]){
        neighborCount = 3;
    }
}

answered Mar 23, 2017 at 14:33

remborg

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1 Comment

FritzFurtz Over a year ago

TypeError: spots[(parseInt(...) + 1)] is undefined. Thanks for the fast answer anyway :)

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