如何总数列？

I have data

A = 100 I wanna output like this

qty | qty_sisa

10    A-10 = 90
20    90-20 = 70
30    70-30 = 40
40    40-40 = 0

You can use foreach

$a = array();
$b = array();
foreach (array_keys($a - $b) as $key) {
    $c[$key] = $a[$key] - $b[$key];
}