Form helper get string value. Then convert numeric value. Other helper functions work properly but only this portion doesn't work.
if(isset($result[$product->id])){
$productArray[$product->id]+= @helper::getCtnQty($product->id,$result[$product->id]); // Error get from this line. but when dd I get value in int form
$singleProductArray[$product->id] = $productArray[$product->id];
<td style="text-align:center;font-weight: 700">
{{@helper::getCtnQty($product->id,$result[$product->id])}}
</td>
}