/// Converts a number to its corresponding alphabetic representation.
///
/// This function takes a positive integer `num` and converts it to a string representing
/// the "alphabetic" value (like Excel column naming). The result is case-sensitive, using uppercase letters.
///
/// # Arguments
/// * `num`: A positive integer representing the number to convert.
///
/// # Returns
/// A `String` representing the alphabetic value corresponding to `num`.
///
/// # Example
/// `1 -> A`, `26 -> Z`, `27 -> AA`