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update variable.md

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sunface
2022-02-28 16:48:07 +08:00
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en/src/variables.md
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@ -1,9 +1,10 @@
# Variables # Variables
### Binding and mutablity ### Binding and mutablity
🌟 fix the error below with least modifying 🌟 A variable can be used only if it has been initialized.
```rust,editable ```rust,editable
// fix the error below with least modifying
fn main() { fn main() {
let x: i32; // uninitialized but using, ERROR ! let x: i32; // uninitialized but using, ERROR !
let y: i32; // uninitialized but also unusing, only warning let y: i32; // uninitialized but also unusing, only warning
@ -11,11 +12,11 @@ fn main() {
} }
``` ```
🌟🌟 fill the blanks in code to make it compile 🌟 Use `mut` to mark a variable as mutable.
```rust,editable ```rust,editable
// fill the blanks in code to make it compile
fn main() { fn main() {
// replace __ with a variable name
let __ = 1; let __ = 1;
__ += 2; __ += 2;
@ -24,9 +25,10 @@ fn main() {
``` ```
### Scope ### Scope
🌟 fix the error below with least modifying 🌟 A scope is the range within the program for which the item is valid.
```rust,editable ```rust,editable
// fix the error below with least modifying
fn main() { fn main() {
let x: i32 = 10; let x: i32 = 10;
{ {
@ -37,9 +39,10 @@ fn main() {
} }
``` ```
🌟🌟 fix the error with the knowledge you grasped 🌟🌟
```rust,editable ```rust,editable
// fix the error
fn main() { fn main() {
println!("{}, world", x); println!("{}, world", x);
} }
@ -50,10 +53,11 @@ fn define_x() {
``` ```
### Shadowing ### Shadowing
🌟🌟 only modify `assert_eq!` to make the `println!` work(print `42` in terminal) 🌟🌟 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.
```rust,editable ```rust,editable
// only modify `assert_eq!` to make the `println!` work(print `42` in terminal)
fn main() { fn main() {
let x: i32 = 5; let x: i32 = 5;
{ {