add solutions for variables

This commit is contained in:
sunface 2022-03-01 21:56:43 +08:00
parent 3b805ff8a4
commit 47d37b6940
2 changed files with 132 additions and 10 deletions

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@ -0,0 +1,121 @@
1.
```rust
fn main() {
let x: i32 = 5; // uninitialized but using, ERROR !
let y: i32; // uninitialized but also unusing, only warning
println!("{} is equal to 5", x);
}
```
2.
```rust
fn main() {
let mut x = 1;
x += 2;
println!("{} is equal to 3", x);
}
```
3.
```rust
fn main() {
let x: i32 = 10;
{
let y: i32 = 5;
println!("The value of x is {} and value of y is {}", x, y);
}
println!("The value of x is {}", x);
}
```
4.
```rust
fn main() {
let x = define_x();
println!("{}, world", x);
}
fn define_x() -> String {
let x = "hello".to_string();
x
}
```
5.
```rust
fn main() {
let x: i32 = 5;
{
let x = 12;
assert_eq!(x, 12);
}
assert_eq!(x, 5);
let x = 42;
println!("{}", x); // Prints "42".
}
```
6.
```rust
fn main() {
let mut x: i32 = 1;
x = 7;
// shadowing and re-binding
let x = x;
// x += 3;
let y = 4;
// shadowing
let y = "I can also be bound to text!";
}
```
7.
```rust
fn main() {
let _x = 1;
}
```
```rust
#[allow(unused_variables)]
fn main() {
let x = 1;
}
```
8.
```rust
fn main() {
let (mut x, y) = (1, 2);
x += 2;
assert_eq!(x, 3);
assert_eq!(y, 2);
}
```
```rust
fn main() {
let (x, y) = (1, 2);
let x = 3;
assert_eq!(x, 3);
assert_eq!(y, 2);
}
```
9.
```rust
fn main() {
let (x, y);
(x,..) = (3, 4);
[.., y] = [1, 2];
// fill the blank to make the code work
assert_eq!([x,y], [3,2]);
}
```

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@ -1,7 +1,7 @@
# Variables
### Binding and mutablity
🌟 A variable can be used only if it has been initialized.
1. 🌟 A variable can be used only if it has been initialized.
```rust,editable
// fix the error below with least modifying
@ -12,7 +12,7 @@ fn main() {
}
```
🌟 Use `mut` to mark a variable as mutable.
2. 🌟 Use `mut` to mark a variable as mutable.
```rust,editable
// fill the blanks in code to make it compile
@ -26,9 +26,10 @@ fn main() {
### Scope
A scope is the range within the program for which the item is valid.
3. 🌟
```rust,editable.
🌟
// fix the error below with least modifying
fn main() {
let x: i32 = 10;
@ -40,10 +41,10 @@ fn main() {
}
```
🌟🌟
4. 🌟🌟
```rust,editable
// fix the error
// fix the error with using of define_x
fn main() {
println!("{}, world", x);
}
@ -56,7 +57,7 @@ fn define_x() {
### Shadowing
You can declare a new variable with the same name as a previous variable, here we can say **the first one is shadowed by the second one.
🌟🌟
5. 🌟🌟
```rust,editable
// only modify `assert_eq!` to make the `println!` work(print `42` in terminal)
@ -74,7 +75,7 @@ fn main() {
}
```
🌟🌟
6. 🌟🌟
```rust,editable
// remove a line in code to make it compile
@ -93,7 +94,7 @@ fn main() {
```
### Unused varibles
fix the warning below with :
7. fix the warning below with :
- 🌟 one way
- 🌟🌟 two ways
@ -110,7 +111,7 @@ fn main() {
```
### Destructuring
🌟🌟 We can use a pattern with `let` to destructure a tuple to separate variables.
8. 🌟🌟 We can use a pattern with `let` to destructure a tuple to separate variables.
> Tips: you can use Shadowing or Mutability
@ -129,7 +130,7 @@ fn main() {
### Destructuring assignments
Introducing in Rust 1.59: You can now use tuple, slice, and struct patterns as the left-hand side of an assignment.
🌟
9. 🌟🌟
> Note: the feature `Destructuring assignments` need 1.59 or higher Rust version