Variables are immutable

We declare variables using the let keyword, and despite calling them variables, in Rust they are immutable by default and the compile enforces this.

fn main() {
    let num = 2;
    println!("{num}");

    num = 3;
    println!("{num}");
}

This is the error message:

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

For more information about this error, try `rustc --explain E0384`.
error: could not compile `immutable-number` (bin "immutable-number") due to 1 previous error

• let