Challenge 1 — Solution

Task: Write a function isEven($number) that returns true if a number is
even and false if it's odd (using the % remainder operator from
Chapter 4). Call it with a few different numbers and echo the results
using var_dump.

<?php
    function isEven($number) {
        return $number % 2 === 0;
    }

    var_dump(isEven(4));
    var_dump(isEven(7));
    var_dump(isEven(0));
?>


Output:
bool(true)
bool(false)
bool(true)

Notes:
- $number % 2 gives the remainder after dividing by 2 - 0 for an even
  number, 1 for an odd one - and === 0 turns that remainder directly
  into a real boolean result.
- The function returns the comparison's own result directly, rather
  than writing a longer if/else that returns true or false separately
  - both work, but returning the comparison itself is more compact.
- 0 correctly counts as even (0 % 2 === 0 is true), which is worth
  testing explicitly since it's an easy edge case to overlook.