Rust

The Rust Programming Language 日本語版 を 自分で学習したときのメモ

2. Programming Guess Game.

1. 新しいプロジェクトを生成する ... v00

実行する

$ cargo new guessing_game Creating binary (application) `guessing_game` package note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html $ cd guessing_game $ tree . . ├── Cargo.toml └── src └── main.rs 2 directories, 2 files

guessing_game/main.rsを変更する

fn main() { println!("Hello, world!"); }

2. 推測を処理する ... v01

read_line 関数は、 「ユーザが標準入力に入力したデータを、文字列に追加する」 という動作を行う。 引数の文字列変数 guess の参照を渡すために & をつけ、 さらに可変にするために mutをつけて、 &mut guessguess と表記している。

read_line 関数は io::Result を返す。 これは enum (列挙)型であり、その列挙子は ok か Err である。 したがって、.expect("...") の部分は返り値の io:Result クラスの expect メソッドが実行される。 Err の expect() メソッドは、実行を中断し、引数として渡されたメッセージを表示する。 ok の expect() メソッドは、正しい返り値を取り出して返す。 今回の read_line() 関数の返り値は、ユーザ入力のバイト数である。

guessing_game/main.rsの変更

*** v00/guessing_game/src/main.rs Sat Jan 24 16:43:55 2026 --- v01/guessing_game/src/main.rs Sun Jan 25 04:56:38 2026 *************** *** 1,3 **** fn main() { ! println!("Hello, world!"); } --- 1,13 ---- + use std::io; + fn main() { ! println!("Guess the number!"); ! println!("Please input your guess."); ! ! let mut guess = String::new(); // ユーザの入力を格納する変数 (可変 mutable) ! io::stdin() ! .read_line(&mut guess) ! .expect("Failed to read line"); ! ! println!("You guessed: {}", guess); }

guessing_game の実行

$ cargo build Compiling guessing_game v0.1.0 (/home/nitta/doc/rust/project/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s $ cargo run Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s Running `target/debug/guessing_game` Guess the number! Please input your guess. 37 You guessed: 37

3. 秘密の数を生成する ... v02
random クレートを利用して機能を追加する。クレートとは Rust ソースコードを集めたものである。 Cargo.toml ファイルの [dependencies] セクションヘッダの下に、に rand クレートと依存関係にあることを記述する。

rand = "0.8.3"

guessing_game/Cargo.tomlの変更

*** v01/guessing_game/Cargo.toml Sat Jan 24 20:47:48 2026 --- v02/guessing_game/Cargo.toml Sat Jan 24 20:52:53 2026 *************** *** 4,6 **** --- 4,7 ---- edition = "2024" [dependencies] + rand = "0.8.3"

ビルドしてみる。

randクレートを加えてビルドする

$ cargo build Updating crates.io index Locking 14 packages to latest Rust 1.93.0 compatible versions Adding cfg-if v1.0.4 Adding getrandom v0.2.17 Adding libc v0.2.180 Adding ppv-lite86 v0.2.21 Adding proc-macro2 v1.0.106 Adding quote v1.0.44 Adding rand v0.8.5 (available: v0.9.2) Adding rand_chacha v0.3.1 Adding rand_core v0.6.4 Adding syn v2.0.114 Adding unicode-ident v1.0.22 Adding wasi v0.11.1+wasi-snapshot-preview1 Adding zerocopy v0.8.33 Adding zerocopy-derive v0.8.33 Downloading crates ... Downloaded cfg-if v1.0.4 Downloaded rand_core v0.6.4 Downloaded rand_chacha v0.3.1 Downloaded ppv-lite86 v0.2.21 Downloaded getrandom v0.2.17 Downloaded rand v0.8.5 Downloaded zerocopy v0.8.33 Downloaded libc v0.2.180 Compiling libc v0.2.180 Compiling zerocopy v0.8.33 Compiling cfg-if v1.0.4 Compiling getrandom v0.2.17 Compiling rand_core v0.6.4 Compiling ppv-lite86 v0.2.21 Compiling rand_chacha v0.3.1 Compiling rand v0.8.5 Compiling guessing_game v0.1.0 (/home/nitta/doc/rust/project/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.03s

cargo は cargo build を最初に実行したときに Cargo.lock ファイルを作成し、 cargo は指示がない限り、指定したバージョンの依存のみを使用する。

クレートをアップグレードしたい場合は、 cargo update コマンドを使用する。 デフォルトでは現在の記述が "0.8.3" の場合は「0.8.3以上0.9.0未満」のバージョンのみを検索する。

4. 乱数を生成する ... v03

1..101 という表現は 1..=100 と同じ意味であり「1から100までの数」を表す。

guessing_game/src/main.rs の変更

*** v02/guessing_game/src/main.rs Sat Jan 24 20:50:57 2026 --- v03/guessing_game/src/main.rs Sun Jan 25 05:25:20 2026 *************** *** 1,7 **** --- 1,11 ---- use std::io; + use rand::Rng; fn main() { println!("Guess the number!"); + let secret_number = rand::thread_rng().gen_range(1..101); + println!("The secret number is: {}", secret_number); + println!("Please input your guess."); let mut guess = String::new(); // ユーザの入力を格納する変数 (可変 mutable)

guessing_game の実行

$ cargo run Compiling guessing_game v0.1.0 (/mnt/hostos/www/html/lec/rust/doc_rust_self/ch02/v03/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s Running `target/debug/guessing_game` Guess the number! The secret number is: 31 Please input your guess. 50 You guessed: 50

5. 推測と秘密の数字を比較する ... v04

guessing_game/src/main.rs の変更

*** v03/guessing_game/src/main.rs Sun Jan 25 05:25:20 2026 --- v04/guessing_game/src/main.rs Sun Jan 25 06:16:40 2026 *************** *** 1,4 **** --- 1,5 ---- use std::io; + use std::cmp::Ordering; use rand::Rng; fn main() { *************** *** 13,17 **** --- 14,27 ---- .read_line(&mut guess) .expect("Failed to read line"); + let guess: u32 = guess.trim().parse() + .expect("Please type a number !"); + println!("You guessed: {}", guess); + + match guess.cmp(&secret_number) { + Ordering::Less => println!("Too small!"), + Ordering::Greater => println!("Too big!"), + Ordering::Equal => println!("You win!"), + } }

guessing_game の実行

$ cargo run Compiling guessing_game v0.1.0 (/mnt/hostos/www/html/lec/rust/doc_rust_self/ch02/v04/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s Running `/mnt/hostos/www/html/lec/rust/doc_rust_self/ch02/v04/guessing_game/target/debug/guessing_game` Guess the number! The secret number is: 95 Please input your guess. 37 You guessed: 37 Too small!

6. ループで複数回の予想を可能にする ... v05

guessing_game/src/main.rs の変更

*** v04/guessing_game/src/main.rs Sun Jan 25 06:16:40 2026 --- v05/guessing_game/src/main.rs Sun Jan 25 06:38:23 2026 *************** *** 6,27 **** println!("Guess the number!"); let secret_number = rand::thread_rng().gen_range(1..101); println!("The secret number is: {}", secret_number); - - println!("Please input your guess."); ! let mut guess = String::new(); // ユーザの入力を格納する変数 (可変 mutable) ! io::stdin() ! .read_line(&mut guess) ! .expect("Failed to read line"); ! let guess: u32 = guess.trim().parse() ! .expect("Please type a number !"); ! println!("You guessed: {}", guess); ! match guess.cmp(&secret_number) { ! Ordering::Less => println!("Too small!"), ! Ordering::Greater => println!("Too big!"), ! Ordering::Equal => println!("You win!"), } ! } --- 6,29 ---- println!("Guess the number!"); let secret_number = rand::thread_rng().gen_range(1..101); println!("The secret number is: {}", secret_number); ! loop { ! println!("Please input your guess."); ! let mut guess = String::new(); // ユーザの入力を格納する変数 (可変 mutable) ! io::stdin() ! .read_line(&mut guess) ! .expect("Failed to read line"); ! let guess: u32 = guess.trim().parse() ! .expect("Please type a number !"); ! println!("You guessed: {}", guess); ! ! match guess.cmp(&secret_number) { ! Ordering::Less => println!("Too small!"), ! Ordering::Greater => println!("Too big!"), ! Ordering::Equal => println!("You win!"), ! } } ! }

guessing_game の実行

$ cargo run Compiling guessing_game v0.1.0 (/mnt/hostos/www/html/lec/rust/doc_rust_self/ch02/v05/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s Running `target/debug/guessing_game` Guess the number! The secret number is: 88 Please input your guess. 50 You guessed: 50 Too small! Please input your guess. 75 You guessed: 75 Too small! Please input your guess. 87 You guessed: 87 Too small! Please input your guess. 94 You guessed: 94 Too big! Please input your guess. 90 You guessed: 90 Too big! Please input your guess. 88 You guessed: 88 You win! Please input your guess. quit )thread 'main' (64610) panicked at src/main.rs:19:14: Please type a number !: ParseIntError { kind: InvalidDigit } note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

7. 推測が正しい場合に終了する ... v06

guessing_game/src/main.rs の変更

*** v05/guessing_game/src/main.rs Sun Jan 25 06:38:23 2026 --- v06/guessing_game/src/main.rs Sun Jan 25 06:44:19 2026 *************** *** 23,29 **** match guess.cmp(&secret_number) { Ordering::Less => println!("Too small!"), Ordering::Greater => println!("Too big!"), ! Ordering::Equal => println!("You win!"), } } } --- 23,32 ---- match guess.cmp(&secret_number) { Ordering::Less => println!("Too small!"), Ordering::Greater => println!("Too big!"), ! Ordering::Equal => { ! println!("You win!"); ! break; ! } } } }

guessing_game の実行

$ cargo run Compiling guessing_game v0.1.0 (/mnt/hostos/www/html/lec/rust/doc_rust_self/ch02/v06/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s Running `target/debug/guessing_game` Guess the number! The secret number is: 16 Please input your guess. 50 You guessed: 50 Too big! Please input your guess. 25 You guessed: 25 Too big! Please input your guess. 12 You guessed: 12 Too small! Please input your guess. 18 You guessed: 18 Too big! Please input your guess. 15 You guessed: 15 Too small! Please input your guess. 16 You guessed: 16 You win!

8. 不正な入力を処理する ... v07

guessing_game/src/main.rs の変更

*** v06/guessing_game/src/main.rs Sun Jan 25 06:44:19 2026 --- v07/guessing_game/src/main.rs Sun Jan 25 08:51:11 2026 *************** *** 15,22 **** .read_line(&mut guess) .expect("Failed to read line"); ! let guess: u32 = guess.trim().parse() ! .expect("Please type a number !"); println!("You guessed: {}", guess); --- 15,24 ---- .read_line(&mut guess) .expect("Failed to read line"); ! let guess: u32 = match guess.trim().parse() { ! Ok(num) => num, ! Err(_) => continue, ! }; println!("You guessed: {}", guess);

guessing_game の実行

$ cargo run Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/guessing_game` Guess the number! The secret number is: 84 Please input your guess. 50 You guessed: 50 Too small! Please input your guess. seventy     ←   不正な入力に対しては再入力を促す Please input your guess. 75 You guessed: 75 Too small! Please input your guess. 87 You guessed: 87 Too big! Please input your guess. 81 You guessed: 81 Too small! Please input your guess. 84 You guessed: 84 You win!

9. 正解の表示を削除する ... v08

guessing_game/src/main.rs の変更

*** v07/guessing_game/src/main.rs Sun Jan 25 08:51:11 2026 --- v08/guessing_game/src/main.rs Sun Jan 25 09:38:06 2026 *************** *** 5,11 **** fn main() { println!("Guess the number!"); let secret_number = rand::thread_rng().gen_range(1..101); ! println!("The secret number is: {}", secret_number); loop { println!("Please input your guess."); --- 5,11 ---- fn main() { println!("Guess the number!"); let secret_number = rand::thread_rng().gen_range(1..101); ! // println!("The secret number is: {}", secret_number); loop { println!("Please input your guess.");

guessing_game の実行

$ cargo run Compiling guessing_game v0.1.0 (/mnt/hostos/www/html/lec/rust/doc_rust_self/ch02/v08/guessing_game) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s Running `target/debug/guessing_game` Guess the number! Please input your guess. 50 You guessed: 50 Too small! Please input your guess. 75 You guessed: 75 Too big! Please input your guess. 63 You guessed: 63 Too small! Please input your guess. 69 You guessed: 69 Too small! Please input your guess. 72 You guessed: 72 Too small! Please input your guess. 74 You guessed: 74 Too big! Please input your guess. 73 You guessed: 73 You win!