PHP calculating two arrays and then add their sum

Question

I want to calculate an array to another array and then add both like this :

   Array1(4,8,7,12);
   Array2(3,6);
   

the result is like this : 3x4+3x8+3x7+3x12+6x4+6x8+6x7+6x12 = 279

I tried with this code and since I'm still new with php I still didn't make any tips I'll be glad thanks in advance

<?php 



tab1(4,8,7,12);
tab2(3,6);
$s=0;
for($i=0; $i<$tab1[3]; $i++){
       for($j=0; $j<$tab2[1]; $j++){
           $s = $s + tab[i] * tab[j];
}
echo "$s";
}
?>

Answer 1

For a more simplistic approach without iteration you can use array_sum on the two arrays.

Example: https://3v4l.org/3gtgE

$a = [4,8,7,12];
$b = [3,6];

$c = array_sum($a) * array_sum($b);
var_dump($c);

Result

int(279)

This works because of the order of operations of:

(3*4) + (3*8) + (3*7) + (3*12) + (6*4) + (6*8) + (6*7) + (6*12) = 279

Equates to the same as the sum of a multiplied by the sum of b:

(4+8+7+12) * (3+6) = 279