Accumulating Numbers in PHP Loops

Let's use a loop to find the sum of integers from 1 to 100. To solve this problem, numbers are iterated through in a loop and their sum is sequentially written into some variable:

php<?php
  $res = 0;
  
  for ($i = 1; $i <= 100; $i++) {
    $res = $res + $i;
  }
  
  echo $res; // the desired sum
?>

The solution can be simplified using the += operator:

php<?php
  $res = 0;
  
  for ($i = 1; $i <= 100; $i++) {
    $res += $i;
  }
  
  echo $res;
?>