1-1

// variables1.rs
// Make me compile!
// Execute `rustlings hint variables1` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    x = 5;
    println!("x has the value {}", x);
}

这题简单,声明的方式出错了

// variables1.rs
// Make me compile!
// Execute `rustlings hint variables1` or use the `hint` watch subcommand for a hint.

fn main() {
    let x = 5;
    println!("x has the value {}", x);
}

1-2

// variables2.rs
// Execute `rustlings hint variables2` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    let x;
    if x == 10 {
        println!("x is ten!");
    } else {
        println!("x is not ten!");
    }
}

Rust不能判断x的类型,指定一下就好了

// variables2.rs
// Execute `rustlings hint variables2` or use the `hint` watch subcommand for a hint.

fn main() {
    let x : i32 = 10;
    if x == 10 {
        println!("x is ten!");
    } else {
        println!("x is not ten!");
    }
}

1-3

// variables3.rs
// Execute `rustlings hint variables3` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    let x: i32;
    println!("Number {}", x);
}

x没有初始化,Rust编译器不允许访问没有初始化的元素

// variables3.rs
// Execute `rustlings hint variables3` or use the `hint` watch subcommand for a hint.

fn main() {
    let x: i32 = 10;
    println!("Number {}", x);
}

1-4

// variables4.rs
// Execute `rustlings hint variables4` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    let x = 3;
    println!("Number {}", x);
    x = 5; // don't change this line
    println!("Number {}", x);
}

Rust默认变量不可变,x=5修改了变量,所以说会拒绝,所以说要让变量可变

// variables4.rs
// Execute `rustlings hint variables4` or use the `hint` watch subcommand for a hint.

fn main() {
    let mut x = 3;
    println!("Number {}", x);
    x = 5; // don't change this line
    println!("Number {}", x);
}

1-5

// variables5.rs
// Execute `rustlings hint variables5` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    let number = "T-H-R-E-E"; // don't change this line
    println!("Spell a Number : {}", number);
    number = 3; // don't rename this variable
    println!("Number plus two is : {}", number + 2);
}

Rust有类型检查,执行运算或者赋值时候要遵循类型的规律,但是Rust可以重新定义同名变量,变量的类型可以发生改变

// variables5.rs
// Execute `rustlings hint variables5` or use the `hint` watch subcommand for a hint.

fn main() {
    let number = "T-H-R-E-E"; // don't change this line
    println!("Spell a Number : {}", number);
    let number = 3; // don't rename this variable
    println!("Number plus two is : {}", number + 2);
}

1-6

// variables6.rs
// Execute `rustlings hint variables6` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

const NUMBER = 3;
fn main() {
    println!("Number {}", NUMBER);
}

const也是一样,当系统不能判断其类型的时候,需要显示说明

// variables6.rs
// Execute `rustlings hint variables6` or use the `hint` watch subcommand for a hint.

const NUMBER : i32 = 3;
fn main() {
    println!("Number {}", NUMBER);
}

2-1

// functions1.rs
// Execute `rustlings hint functions1` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    call_me();
}

这一题我们需要自己声明一个无参数无返回值的函数.fn 名字 (){}

// functions1.rs
// Execute `rustlings hint functions1` or use the `hint` watch subcommand for a hint.

fn call_me(){
    println!("Hello World");
}
fn main() {
    call_me();
}

2-2

// functions2.rs
// Execute `rustlings hint functions2` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    call_me(3);
}

fn call_me(num:) {
    for i in 0..num {
        println!("Ring! Call number {}", i + 1);
    }
}

有参数的函数.参数在括号里面,用逗号隔开,名字:类型

// functions2.rs
// Execute `rustlings hint functions2` or use the `hint` watch subcommand for a hint.

fn main() {
    call_me(3);
}

fn call_me(num:i32) {
    for i in 0..num {
        println!("Ring! Call number {}", i + 1);
    }
}

2-3

// functions3.rs
// Execute `rustlings hint functions3` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    call_me();
}

fn call_me(num: u32) {
    for i in 0..num {
        println!("Ring! Call number {}", i + 1);
    }
}

很难看不出来是函数调用的时候漏传实参了,补上实参即可

2-4

// functions4.rs
// Execute `rustlings hint functions4` or use the `hint` watch subcommand for a hint.

// This store is having a sale where if the price is an even number, you get
// 10 Rustbucks off, but if it's an odd number, it's 3 Rustbucks off.
// (Don't worry about the function bodies themselves, we're only interested
// in the signatures for now. If anything, this is a good way to peek ahead
// to future exercises!)

// I AM NOT DONE

fn main() {
    let original_price = 51;
    println!("Your sale price is {}", sale_price(original_price));
}

fn sale_price(price: i32) -> {
    if is_even(price) {
        price - 10
    } else {
        price - 3
    }
}

fn is_even(num: i32) -> bool {
    num % 2 == 0
}

函数返回返回值的方法 就是 -> 返回值类型 ,返回值可以是最后一条语句的值(这个语句不要加分号),也可以定义return

给sale_price的->后面添加上返回值类型i32即可

2-5

// functions5.rs
// Execute `rustlings hint functions5` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

fn main() {
    let answer = square(3);
    println!("The square of 3 is {}", answer);
}

fn square(num: i32) -> i32 {
    num * num;
}

定义返回值不是这么定义的,一般是语句或者是return,所以说要么改成return num * num;要么去掉分号.一个块中最后一条语句去掉分号、这个可以称为块尾,就是返回值

3-1

写一个bigger函数,判断返回a和b中大的那个:

pub fn bigger(a: i32, b: i32) -> i32 {
    // Complete this function to return the bigger number!
    // Do not use:
    // - another function call
    // - additional variables
    if a > b{
        a
    }
    else{
        b
    }
}

3-2

修改这个函数,使得可以编译并且能够通过测试

pub fn foo_if_fizz(fizzish: &str) -> &str {
    if fizzish == "fizz" {
        "foo"
    } else {
        1
    }
}

第一个是,返回的是&str,不能返回1这个数字,然后修改逻辑能够通过测试就好

pub fn foo_if_fizz(fizzish: &str) -> &str {
    if fizzish == "fizz" {
        "foo"
    } else if fizzish == "fuzz" {
        "bar"
    }
    else{
        "baz"
    }
}

分类: 杂项

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