Challenge 3 — Solution

Task: Create a global variable $counter = 0. Write a function that
creates its own local variable also called $counter, sets it to 100,
and echoes it. After calling the function, echo the original global
$counter to demonstrate it was never affected — add a comment
explaining why.

<?php
    $counter = 0;

    function setLocalCounter() {
        $counter = 100;   // this is a completely separate, local $counter
        echo "Inside the function: $counter<br>";
    }

    setLocalCounter();

    // The global $counter is untouched, because functions have their own
    // local scope - the $counter inside setLocalCounter() never referred
    // to the outer one at all, despite sharing the exact same name.
    echo "Global counter after calling the function: $counter";
?>


Output:
Inside the function: 100
Global counter after calling the function: 0

Notes:
- Both variables share the name $counter, but PHP treats them as two
  entirely separate variables because one lives in the global scope and
  the other lives inside setLocalCounter()'s own local scope.
- Setting the local $counter to 100 has zero effect on the global one -
  this is exactly the "two boxes" diagram from the chapter, just with a
  counter instead of $x.
- Without a global $counter; declaration inside the function (which
  this solution deliberately doesn't use), there is no way for the
  function's own assignment to reach outside its own scope.