PHP siklda massivni o'zgartirish

Bizda quyidagi sonlar massivi berilgan bo'lsin:

php<?php
  $arr = [1, 2, 3, 4, 5];
?>

Keling, ushbu massivning har bir elementini ikki baravar oshiramiz:

php<?php
  $arr = [1, 2, 3, 4, 5];
  
  $arr[0] = $arr[0] * 2;
  $arr[1] = $arr[1] * 2;
  $arr[2] = $arr[2] * 2;
  $arr[3] = $arr[3] * 2;
  $arr[4] = $arr[4] * 2;
  
  var_dump($arr); // [2, 4, 6, 8, 10] ni chiqaradi
?>

Endi xuddi shu narsani siklda bajaramiz:

php<?php
  $arr = [1, 2, 3, 4, 5];
  $length = count($arr);
  
  for ($i = 0; $i < $length; $i++) {
    $arr[$i] = $arr[$i] * 2;
  }
  
  var_dump($arr); // [2, 4, 6, 8, 10] ni chiqaradi
?>