简单的 php 对于每个它都不能很好地相加

Question

there is 3 positions in $input['order_items'] , i am extracting $orderItem['subtotal'] which gives to me the total of a product and $orderItem['subtotal_tax'] which gives to me total tax of such product, what i am doing is adding subtotal with subtotal_tax , the problem is the function is not summing or adding correctly the value, for example in first position i got this:

"total": "13302",
      "total_tax": "0",

second position i got this:

"total": "9711",
      "total_tax": "0",

third position i got this:

"subtotal": "14022",
      "subtotal_tax": "0",

as result of the sum it should give to me this:

37035

but i am getting:

28044

must ask, why? and how to correct it? thanks in foward

$i = 0;
$nvCantVar = 0;
$subtotal = 0;
$subtotal_tax = 0;
$NotaVentaDetalleDTO = '';
foreach ($input['order_items'] as $orderItem) {
    $i++;

    $subtotal = $orderItem['subtotal'];
    $subtotal_tax = $orderItem['subtotal_tax'];
    $nvCantVar =  $subtotal + $subtotal_tax;  
}

$nvCantVar = $nvCantVar + $nvCantVar;

why could this be happening?

Answer 1

You are using a scalar variable in the loop and therefore over writing the accumulator with the last value each time rather than accumulating a grand total.

Instead of = use += to add each value to the existing value of the accumulator in the loop

$nvCantVar = 0;

foreach ($input['order_items'] as $orderItem) {
    $nvCantVar +=  $orderItem['subtotal'] + $orderItem['subtotal_tax'];  
}

echo $nvCantVar;

Answer 2

Your PHP code isn't following the logic you want at all.

Firstly why the $i what is this being used for? Secondly your code is looping, overriding the value of $nvCantVar and then simply adding the final value of this variable to itself to get the new value.

So the math it is doing is:

$nvCantVar = 14022 + 14022

What you want is something like

$nvCantTotal = 0;
foreach ($input['order_items'] as $orderItem) {
  $subtotal = $orderItem['subtotal'];
  $subtotal_tax = $orderItem['subtotal_tax'];
  $nvCantTotal += $subtotal + $subtotal_tax;  
}