Random number

Generate a secret number with the rand crate.

A random number

Rust's standard library has no random number generator; the rand crate is used for that. The dependency is added to Cargo.toml and cargo build downloads it:

[dependencies]
rand = "0.8"

use rand::Rng;

let gizli = rand::thread_rng().gen_range(1..=100);

The gen_range method comes from the Rng trait; it can't be called until the trait is brought into scope (use rand::Rng;).

Without a crate: a simple generator

Since external crates can't be downloaded in the exercise environment, we can write a simple linear congruential generator (LCG) for learning purposes. The same seed always gives the same sequence, which makes testing easy:

let mut tohum: u64 = 42;
tohum = (tohum * 1103515245 + 12345) % 2147483648;
let gizli = tohum % 100 + 1;   // 1..=100

This method is not suitable for security; use rand in real programs.

Exercise Generate the secret

Start with let mut tohum: u64 = 42;. Apply tohum = (tohum * 1103515245 + 12345) % 2147483648; once, then compute the secret with tohum % 100 + 1 and print it as Gizli sayı: ....

Show example solution

fn main() {
    let mut tohum: u64 = 42;
    tohum = (tohum * 1103515245 + 12345) % 2147483648;
    let gizli = tohum % 100 + 1;
    println!("Gizli sayı: {}", gizli);
}

Test yourself

Which values can <code>gen_range(1..=100)</code> produce?
- 0 to 99
- 1 to 99
- Any u32
- 1 to 100, both included
Show answer

1 to 100, both included — ..= is an inclusive range; 100 is included too.

Bring the trait into scope

use rand::____;

let gizli = rand::thread_rng().gen_range(1..=100);

Show answer

use rand::Rng;

let gizli = rand::thread_rng().gen_range(1..=100);

Piece and meaning

rand = "0.8"

Dependency
thread_rng()

Generator
gen_range(1..=100)

Between 1 and 100
% 100 + 1

Reduces to the range

Next lesson: Loop and exit

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