Challenge 2: Finding the First Even Number — Possible Solution
====================================================================

fn find_first_even(numbers: &[i32]) -> Option<i32> {
    for &n in numbers {
        if n % 2 == 0 {
            return Some(n);
        }
    }
    None
}

fn main() {
    let nums = [1, 3, 7, 8, 9];

    match find_first_even(&nums) {
        Some(n) => println!("First even number: {}", n),
        None => println!("No even number found"),
    }
}

WHY THIS WORKS AS AN ANSWER
------------------------------
find_first_even returns Option<i32> rather than a plain i32, because
there genuinely might not be an even number in the slice — exactly the
"value might be absent" situation this chapter's Option<T> section
described. Returning Some(n) the moment an even number is found wraps
the real value; falling through the entire loop without finding one
returns None instead — there is no way to accidentally return "nothing"
without it being explicitly represented as one of these two variants.

The calling code's match forces handling BOTH possibilities: Some(n)
extracts and prints the found number, None prints a fallback message
— the compiler would refuse to compile this match if either arm were
missing, guaranteeing the "no even number" case can never be silently
ignored the way a Go function returning a zero-value int (0) could be
mistaken for a genuinely found value of 0.