Rust Practice Exercises

Fibonacci Sequence in Rust

Build the Fibonacci numbers with a loop, a tuple swap and a vector.

Beginner
2 min read
1 runnable example

What you'll learn

A loop with two variables
(a, b) = (b, a + b)
Why u64

Run code →

The first numbers

5 = 2 + 3

Each number is the sum of the two before

Each Fibonacci number is the sum of the two before it, starting from 0 and 1. Build the first numbers of the sequence in a vector.

a and b hold two neighbouring numbers. (a, b) = (b, a + b) moves both one step forward in a single assignment. u64 is used because Fibonacci numbers grow quickly: the 50th no longer fits in 32 bits.

Key points

Start from 0 and 1.
One tuple assignment moves both values.
u64 holds much larger numbers than u32.

Runnable Rust example

Rust

Run code →

main.rs

fn fibonacci(count: usize) -> Vec<u64> {
    let mut sequence = Vec::with_capacity(count);
    let (mut a, mut b) = (0u64, 1u64);
    for _ in 0..count {
        sequence.push(a);
        (a, b) = (b, a + b);
    }
    sequence
}

fn main() {
    println!("{:?}", fibonacci(10));
    println!("50th: {}", fibonacci(50)[49]);
}

Get a Run button for this example Result of running the code

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
50th: 7778742049

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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