Question

I created a for(…) cycle where I plan to go through the values of an array and use those values to accumulate them in another array, but I’m getting a notice from Apache that says Notice: Undefined offset: …. The code I’m using is something like this:

for ($a=0;$a<count($original_array);$a++){
    $accumulate_array[$a] += $original_array[$a]
}

I think the notice comes from the part where I do the “+=” because it’s doing something like:

$accumulate_array[$a] = $accumulate_array[$a] + $original_array[$a]

And it’s referencing a value that still doesn’t exist, I think.

Answer 1

You’re correct, the notice is because of this line:

$accumulate_array[$a] += $original_array[$a];

Because it expands to:

$accumulate_array[$a] = $accumulate_array[$a] + $original_array[$a];

And $accumulate_array[$a] is undefined, while it’s trying to grab that value. So, if you’re creating a running sum, you probably want to initialize it to zero, like so:

if( !isset( $accumulate_array[$a] )) $accumulate_array[$a] = 0;
$accumulate_array[$a] = $accumulate_array[$a] + $original_array[$a];