Deleting Sessions in PHP

Sometimes we may need to delete a specific session variable without affecting the others. This is done using the unset function:

php<?php
  unset($_SESSION['var']);
?>

After executing such code, our variable will become null:

php<?php
  var_dump($_SESSION['var'); // will output null
?>

Задание 1

Here is the counter code from the previous lesson:

php<?php
  session_start();
  
  if (!isset($_SESSION['counter'])) {
    $_SESSION['counter'] = 1;
  } else {
    $_SESSION['counter']++;
  }
  
  echo $_SESSION['counter'];
?>

Modify this code so that when the counter reaches the value of 10, the count starts over.