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

This is actually a piece of cake. I am not sure what tab1 means but I assume you are trying to use this function to get an array of desired(input) numbers.

Using a foreach loop to loop over the two arrays, I came up with the code below:

<?php
$a = [4,8,7,12];
$b = [3,6];
$sum = 0;
foreach ($b as $valueInB) {
    foreach ($a as $valueInA) {
        $sum += $valueInA * $valueInB;
    }
}
echo $sum;
?>

which results in:

279

if you are insisting on using a for loop you can run the code below to get the same result:

<?php
$a = [4,8,7,12];
$b = [3,6];
$sum = 0;
$bLength = count($b);
$aLength = count($a);
for ($i=0; $i < $bLength  ; $i++) { 
    $valueInB = $b[$i];
    for ($j=0; $j < $aLength ; $j++) { 
        $valueInA = $a[$j];
        $sum += $valueInA * $valueInB;
    }
} 
echo $sum;
?>

Please note that you should use the count outside of the loop because looping over the array and calling count each time is not an efficient way. (Thanks to Will B for the comment)