# Having problem understanding the accumalator function

Tell us what’s happening:
so my problem is with the accumulator
see: freeCodeCamp Challenge Guide: Iterate Through an Array with a For Loop
in the previous one we used the total
which basiscallly means total = total + i

``````total += myArr[i]
``````

so then since in this one we needed to add them together should’t it be :

``````product += [i] + [x];
or
a = a [i];
b = b[x];
product = a + b;
``````

So why is this not working?

``````
function multiplyAll(arr) {
var product = 1;
// Only change code below this line
for(var i = 0; arr.lenght; i++){
for (var x = 0; x <arr[i].length; x++){
product += [i] + [x];
}

}
// Only change code above this line
return product;
}

multiplyAll([[1,2],[3,4],[5,6,7]]);

``````

User Agent is: `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.183 Safari/537.36`.

Challenge: Nesting For Loops

You can’t add arrays together, you’ve written something that starts `1 += [0] + [0]`, which makes no sense and will error at that point.

1 Like

You have a typo in your loop declaration (`lenght` instead of `length`), but that aside - I’m not sure what this line is supposed to do:

`product += [i] + [x];`

• The challenge asks you to calculate the total product, but your code tries to calculate the sum instead.

• The `product` variable is of type `number`, so you can’t add an array to it (as stated above already). Think about what values exactly you should multiply to get the total product

Hope that gave a hint.

1 Like