Rust学习笔记 - Guessing Number

[citrus327]

Guessing Number 程序

use std::io;

fn main() {
    println!("Guess the number!");

    println!("Please input your guess.");

    // created a mutable variable that is currently bound to a new, empty instance of a String
    let mut guess = String::new();

    io::stdin()
        .read_line(&mut guess)
        .expect("Failed to read line");

    println!("You guessed: {}", guess);
}

• Prelude: 翻译为前奏，默认rust会引入一些default包，如果不在默认返回需要显式引入

• mut ：mutable的意思在变量名前加上mut代表这个变量可以被mutate

• String::new():可以理解成是call了String的一个static method

• &: reference

• 链式调用建议换行

• read_line返回的是一个io:Result的变量，可以用expect函数来处理异常情况，如果不处理，会给相应的warning让你处理。

  If this instance of io::Result is an Err value, expect will cause the program to crash and display the message that you passed as an argument to expect. If the read_line method returns an Err, it would likely be the result of an error coming from the underlying operating system. If this instance of io::Result is an Ok value, expect will take the return value that Ok is holding and return just that value to you so you can use it.

• println!("You guessed: {}", guess);可以使用{}做为占位符，如果有{}则必传相应参数

拓展Guessing Number

• 使用rand crates去生成随机数

  let secret_number = rand::thread_rng().gen_range(1, 101);

• 比较需要将stdin的输入转成int
  let guess: u32 = guess.trim().parse().expect("Please type a number!");
:u32是一种类型的anotation，告知parse函数需要转换成这种格式的数字

• 代码里如果有已经定义过的变量，可以重复申明

  let mut guess = String::new();
  // ...
  let guess: i32 = guess.trim().parse().expect("Please type a number!");

  This feature is often used in situations in which you want to convert a value from one type to another type

  这种行为在Rust内称为Shadowing

• 使用match进行数值比较

  match guess.cmp(&secret_number) {
    Ordering::Less => println!("Too small!"),
    Ordering::Greater => println!("Too big!"),
    Ordering::Equal => println!("You win!"),
  }

• 添加循环，让用户持续输入直到win

• 容错处理 - 如果输入的不是数字，parse成数字会报错，这种可以用match来处理。

  let guess: u32 = match guess.trim().parse() {
    Ok(num) => num,
    Err(_) => continue,
  };