Booleans and chars

A bool is either true or false. Combine booleans with && (and), || (or) and ! (not). Comparisons like ==, < and >= produce a bool. The operators && and || short-circuit: the right side runs only if needed.

let year = 2024;
let divisible_by_four = year % 4 == 0;
let not_century = year % 100 != 0;
println!("{}", divisible_by_four && not_century); // true

A char is a single Unicode character in single quotes: 'a', '7', 'ß', '🦀'. It takes 4 bytes, and is not the same as a one-letter string ("a"). Useful methods:

• c.is_alphabetic(), c.is_numeric() and c.is_whitespace() return bool.
• c.to_ascii_uppercase() and c.to_ascii_lowercase() return a new char and leave non-letters untouched.

let c = 'q';
let big = if c.is_alphabetic() { c.to_ascii_uppercase() } else { c };
// big is 'Q'

Your task

Write these public functions:

• is_leap_year(year: u32) -> bool: a leap year is divisible by 4, except years divisible by 100, unless they are also divisible by 400. So 2000 and 2024 are leap years; 1900 and 2023 are not.
• capitalize_letter(c: char) -> char: uppercase the character if it is a letter, otherwise return it unchanged.
• is_vowel(c: char) -> bool: true for a e i o u in either case.