Rust Variables and Constats

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Index

1. Rust Variable Declaration
2. Change Value of a Variable
3. Mutability in Rust

Related: Rust variable naming rules Official documentation: link

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Rust Variable Declaration

We use the let keyword to declare a variable in Rust.

let age = 31;

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Change Value of a Variable

By default, Rust variables are immutable, which means we cannot change the value of a variable once it is defined. Let’s see an example,

fn main() {
    // declare a variable with value 1
    let x = 1;
    println!("x = {}", x);
 
    // change the value of variable x
    x = 2;
    println!("x = {}", x);
}

When we run this code, we will get an error. This is because we are trying to change the value of the x variable from 1 to 2.

output:

error[E0384]: cannot assign twice to immutable variable `x`
 --> main.rs:7:5
  |
3 |     let x = 1;
  |         -
  |         |
  |         first assignment to `x`
  |         help: consider making this binding mutable: `mut x`
...
7 |     x = 2;
  |     ^^^^^ cannot assign twice to immutable variable

To solve this problem, Rust allows us to create mutable variables.

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Mutability in Rust

We use the mut keyword before the variable name to create a mutable variable. For example,

let mut x = 1;

Here, x is a mutable variable. Now we can change the value of x.

Example:

fn main() {
  // declare a mutable variable with value 1
  let mut x = 1;
  println!("Value of x = {}", x);

   // change the value of variable x
   x = 2;
   println!("Updated value of x = {}", x);
}

output:

Value of x = 1
Updated value of x = 2

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Global Variables

Rust Global Variables

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Official documentation: link

Link to original

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