150 lines
2.8 KiB
Markdown
150 lines
2.8 KiB
Markdown
# Variables
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### Binding and mutablity
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1. π A variable can be used only if it has been initialized.
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```rust,editable
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// fix the error below with least modifying
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fn main() {
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let x: i32; // uninitialized but using, ERROR !
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let y: i32; // uninitialized but also unusing, only warning
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println!("{} is equal to 5", x);
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}
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```
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2. π Use `mut` to mark a variable as mutable.
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```rust,editable
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// fill the blanks in code to make it compile
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fn main() {
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let __ = 1;
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__ += 2;
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println!("{} is equal to 3", x);
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}
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```
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### Scope
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A scope is the range within the program for which the item is valid.
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3. π
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```rust,editable
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// fix the error below with least modifying
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fn main() {
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let x: i32 = 10;
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{
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let y: i32 = 5;
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println!("The value of x is {} and value of y is {}", x, y);
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}
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println!("The value of x is {} and value of y is {}", x, y);
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}
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```
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4. ππ
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```rust,editable
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// fix the error with using of define_x
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fn main() {
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println!("{}, world", x);
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}
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fn define_x() {
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let x = "hello";
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}
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```
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### Shadowing
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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.
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5. ππ
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```rust,editable
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// only modify `assert_eq!` to make the `println!` work(print `42` in terminal)
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fn main() {
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let x: i32 = 5;
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{
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let x = 12;
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assert_eq!(x, 5);
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}
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assert_eq!(x, 12);
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let x = 42;
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println!("{}", x); // Prints "42".
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}
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```
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6. ππ
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```rust,editable
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// remove a line in code to make it compile
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fn main() {
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let mut x: i32 = 1;
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x = 7;
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// shadowing and re-binding
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let x = x;
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x += 3;
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let y = 4;
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// shadowing
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let y = "I can also be bound to text!";
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}
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```
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### Unused varibles
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1. fix the warning below with :
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- π only one solution
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- ππ two distinct solutions
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> Note: none of the solutions is to remove the line `let x = 1`
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```rust,editable
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fn main() {
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let x = 1;
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}
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// warning: unused variable: `x`
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```
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### Destructuring
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8. ππ We can use a pattern with `let` to destructure a tuple to separate variables.
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> Tips: you can use Shadowing or Mutability
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```rust,editable
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// fix the error below with least modifying
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fn main() {
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let (x, y) = (1, 2);
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x += 2;
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assert_eq!(x, 3);
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assert_eq!(y, 2);
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}
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```
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### Destructuring assignments
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Introducing in Rust 1.59: You can now use tuple, slice, and struct patterns as the left-hand side of an assignment.
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9. ππ
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> Note: the feature `Destructuring assignments` need 1.59 or higher Rust version
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```rust,editable
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fn main() {
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let (x, y);
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(x,..) = (3, 4);
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[.., y] = [1, 2];
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// fill the blank to make the code work
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assert_eq!([x,y], __);
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}
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```
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> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it
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