Rust lang のチュートリアル3章5項の自分の解答

以下を実装したプログラムです

• 温度を華氏と摂氏で変換する。
• フィボナッチ数列のn番目を生成する。
• クリスマスキャロルの定番、"The Twelve Days of Christmas"の歌詞を、 曲の反復性を利用して出力する。https://doc.rust-jp.rs/book/second-edition/ch03-05-control-flow.html

以下コードです。 variables というプロジェクトで実装しています。

入力値のオーバーフローは無視しています。例えば、 get_specific_fib(50) などすると返り値が i32 を超えるのでエラーになります。とくにハンドリングはしていません。

    fn main() {
        let celsius_to_fahrenheit = celsius_to_fahrenheit(35.5);
        println!("celsius_to_fahrenheit: {}", celsius_to_fahrenheit);

        let get_specific_fib = get_specific_fib(7);
        println!("get_specific_fib: {}", get_specific_fib);

        println!("

");
        the_twelve_days_of_christmas();
    }

    fn celsius_to_fahrenheit(celsius: f64) -> f64 {
        (celsius * 9.0 / 5.0) + 32.0
    }

    fn get_specific_fib(index: i32) -> i32 {
        if index == 1 {
            return 0;
        } else if index == 2 {
            return 1;
        }

        let mut first  = 0;
        let mut second = 1;

        let mut cnt = 2;
        let mut acc; // acc = 0 にすると何故か warning がでる

        loop {
            cnt = cnt + 1;

            acc = first + second;
            if cnt == index {
                break;
            }

            first = second;
            second = acc;
        }

        acc
    }

    fn the_twelve_days_of_christmas() {
        let fix_part = "On the first day of Christmas,
my true love sent to me";

        let arr_part = [
            "And a partridge in a pear tree.",
            "Two turtle doves,",
            "Three French hens",
            "Four calling birds",
            "Five golden rings",
            "Six geese a-laying",
            "Seven swans a-swimming",
            "Eight maids a-milking",
            "Nine ladies dancing",
            "Ten lords a-leaping",
            "Eleven pipers piping",
            "Twelve drummers drumming",
        ];

        let song_part = 12;
        let mut start = 1;
        let mut index;

        while start != (song_part-1) {
            println!("{}", fix_part);

            index = start;
            while index >= 1 {
                if start == 1 {
                    println!("A partridge in a pear tree.");
                } else {
                    println!("{}", arr_part[index - 1]);
                }
                index = index - 1;
            }

            start = start + 1;
            println!("
");
        }
    }

以下実行結果です

    /home/nao000dotcom/variables # cargo run
       Compiling variables v0.1.0 (/home/nao000dotcom/variables)
        Finished dev [unoptimized + debuginfo] target(s) in 1.21s
         Running `target/debug/variables`
    celsius_to_fahrenheit: 95.9
    get_specific_fib: 8



    On the first day of Christmas,
    my true love sent to me
    A partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Five golden rings
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Six geese a-laying
    Five golden rings
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Seven swans a-swimming
    Six geese a-laying
    Five golden rings
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Eight maids a-milking
    Seven swans a-swimming
    Six geese a-laying
    Five golden rings
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Nine ladies dancing
    Eight maids a-milking
    Seven swans a-swimming
    Six geese a-laying
    Five golden rings
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    On the first day of Christmas,
    my true love sent to me
    Ten lords a-leaping
    Nine ladies dancing
    Eight maids a-milking
    Seven swans a-swimming
    Six geese a-laying
    Five golden rings
    Four calling birds
    Three French hens
    Two turtle doves,
    And a partridge in a pear tree.


    /home/nao000dotcom/variables #