Common Programming Concepts
Comment
// 单行注释
/*
多行注释
*/
Variables and Mutability
let
rust 基本变量默认不可变
使用 let 关键字声明变量
let x = 5;
println!("x = {x}");// 输出 x = 5
// x = 6; // Error! cannot assign twice to immutable variable
也可以显示声明变量类型
格式 data_name: type
let x: i32 = 5;
println!("x = {x}");// 输出 x = 5
变量名小写，大写 warning 警告！
let X = 5;
println!("{}", X);
// warning: variable `X` should have a snake case name
/*
help: convert the identifier to snake case (notice the capitalization): `x`
|
= note: `#[warn(non_snake_case)]` on by default
*/
mut
使用 mut 关键字表示变量可变
let mut y = 5;
println!("y = {y}");// y = 5
y = 6;
println!("y = {y}");// y = 6
const
使用 const 关键字表明常量 (constants)
必须显示声明常量类型
const YEAR : i32 = 2024;
println!("YEAR = {YEAR}");
常量名一般全部大写，小写 warning 警告！
const Year : i32 = 2024;
println!("YEAR = {Year}");
// constant `Year` should have an upper case name
/*
help: convert the identifier to upper case: `YEAR`
|
= note: `#[warn(non_upper_case_globals)]` on by default
*/
shadowing
变量名与前面变量名相同，后面数据覆盖前面
let s = 5;
println!("s = {s}");// s = 5
let s = s + 1;// 覆盖前面的内容
println!("s = {s}");// s = 6
let s = s * 2;
println!("s = {s}");// s = 12
let s = " ";
println!("s = {s}");// s =
let s = s.len();// 类型可变
println!("s = {s}");// s = 4
吐槽：感觉 shadowing 会造成错误，为什么不直接报错，不小心用了相同名字，前面数据就会被覆盖，这个设计感觉没用
Data Types
Integer Types
| Length | Signed | Unsigned |
|---|---|---|
| 8-bit | i8 |
u8 |
| 16-bit | i16 |
u16 |
| 32-bit | i32 |
u32 |
| 64-bit | i64 |
u64 |
| 128-bit | i128 |
u128 |
| arch | isize |
usize |
Integer Literals in Rust
| Number literals | Example |
|---|---|
| Decimal | 98_222 |
| Hex | 0xff |
| Octal | 0o77 |
| Binary | 0b1111_0000 |
Byte (u8 only) |
b'A' |
数据 overflow 会导致 error
let x: i8 = 100;
let y: i8 = 100;
let z: i8 = x + y;
println!("{}", z);
// i8 [-127, 128]
/*
error: this arithmetic operation will overflow
attempt to compute `100_i8 + 100_i8`, which would overflow
|
= note: `#[deny(arithmetic_overflow)]` on by default
*/
Floating-Point Types
| Length | Type |
|---|---|
| 32-bit | f32 |
| 64-bit | f64 |
Numeric Operations
// addition
let sum = 5 + 10;
// subtraction
let difference = 95.5 - 4.3;
// multiplication
let product = 4 * 30;
// division
let quotient = 56.7 / 32.2;
let truncated = -5 / 3; // Results in -1
// remainder
let remainder = 43 % 5;
应该和 C++ 是一样的
The Boolean Type
let t = true;
let f: bool = false;// with explicit type annotation
println!("{t} {f}");// true false
The Character Type
let c = 'z';
let z: char = 'ℤ'; // with explicit type annotation
let heart_eyed_cat = '😻';
println!("{c} {z} {heart_eyed_cat}");// z Z 😻
Compound Types
Tuple
元组内数据类型可以不同
可以取出来访问，或用下标访问 data_name.index
let x: (i32, f32, bool) = (1, 2.0, false);
let (a, b, c) = x;
println!("{a} {b} {c}");
println!("{} {} {}", x.0, x.1, x.2);
越界会 Error!
println!("{} {} {}", x.0, x.1, x.3);
// error[E0609]: no field `3` on type `(i32, f32, bool)`
直接打印元组
println!("{x}");// Error
/*
error[E0277]: `(i32, f32, bool)` doesn't implement `std::fmt::Display`
*/
Array
类型必须一样
使用 [] 来表示
let x = [1, 2, 3, 4, 5];
// [type; size]
let x: [i32; 5] = [1, 2, 3, 4, 5];// with explicit type annotation
声明相同数据的数组
// [val; size] init with same val
let x = [0; 5];
注意 [] 内是 ;
访问数组元素，使用 data_name[index]
println!("{}", x[0]);
println!("{}", x[5]);// this operation will panic at runtime index out of bounds: the length is 5 but the index is 5
Functions
使用关键字 fn 来声明函数
不需要像 C++ 一样先声明后调用
fn fn_name(Parameters) -> type {
}
-> type 可不写
例如
println!("{}", test(10));
fn test(n: i32) -> i32 {
return n;
}
这样也可
fn test(n: i32) -> i32 {
// expression
n// 注意无;
}
// 若添加 ;
// expected `i32`, found `()`
函数名小写，大写 warning 警告！
fn TEST(n: i32) -> i32 {
n
}
//warning: function `TEST` should have a snake case name
/*
help: convert the identifier to snake case: `test`
|
= note: `#[warn(non_snake_case)]` on
*/
Control Flow
if
if 后条件必须为 bool 类型！！！
let number = 3;
if number < 5 {
println!("condition was true");
} else {
println!("condition was false");
}
if number {
println!("condition was true");
} else {
println!("condition was false");
}
// error[E0308]: mismatched types
// expected `bool`, found integer
多条件用 && 或 || 连接
let number = 3;
if 3 < number && number < 5 {
println!("condition was true");
} else {
println!("condition was false");
}
else if 使用
let number = 6;
if number % 4 == 0 {
println!("number is divisible by 4");
} else if number % 3 == 0 {
println!("number is divisible by 3");
} else if number % 2 == 0 {
println!("number is divisible by 2");
} else {
println!("number is not divisible by 4, 3, or 2");
}
let + if
if 和 else 后的类型必须一样
有点像三目运算符复制
let condition = true;
let number = if condition { 5 } else { 6 };
println!("The value of number is: {number}");
let number = if condition { 5 } else { "six" };
// expected integer, found `&str
loop
一直循环
break 跳出循环，continue 继续下一次循环
loop {
println!("again!");
}// 一直输出 again
while
基本形式
while condition {}
例如
while x > 0 {
x -= 1;
println!("{x}");
}
for
基本形式
for x in item {}
例如
for x in [3; 5] { // 产生长度为 5 的全是 3 的数组
println!("{x}");
}
for i in (1..4) { // (l..r) 表示区间 [1, 4) 不含 4
println!("{i}");
}
