Rust Examples — Runnable Code Snippets

Practical, runnable Rust snippets. Click any example to open it in the interactive Rust playground, then edit the code and compile it with full compiler diagnostics.

hello world + fibonacci

fn main() {
    println!("Hello from Rust!");

    for i in 0..10 {
        println!("fib({}) = {}", i, fib(i));
    }
}

fn fib(n: u64) -> u64 {
    if n < 2 {
        n
    } else {
        fib(n - 1) + fib(n - 2)
    }
}

Run a Rust program that prints Hello World and computes Fibonacci numbers.

Open in Rust playground

HashMap word count

use std::collections::HashMap;

fn main() {
    let words = ["banana", "apple", "cherry", "apple", "banana", "apple"];

    // Count occurrences with a HashMap.
    let mut counts: HashMap<&str, i32> = HashMap::new();
    for w in &words {
        *counts.entry(w).or_insert(0) += 1;
    }

    // Sort keys for stable output.
    let mut keys: Vec<&&str> = counts.keys().collect();
    keys.sort();

    for k in keys {
        println!("{:<8} {}", k, counts[*k]);
    }
}

Count word occurrences using a HashMap in Rust.

Open in Rust playground

iterators (map/filter/sum)

fn main() {
    let nums = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

    let sum_of_even_squares: i32 = nums
        .iter()
        .filter(|&&x| x % 2 == 0)
        .map(|&x| x * x)
        .sum();

    println!("nums: {:?}", nums);
    println!("sum of even squares: {}", sum_of_even_squares);

    let doubled: Vec<i32> = nums.iter().map(|x| x * 2).collect();
    println!("doubled: {:?}", doubled);
}

Transform and reduce a vector using Rust iterator adapters.

Open in Rust playground