Fibonacci in Rust

Published on 05 October 2018 (Updated: 08 May 2023)

Welcome to the Fibonacci in Rust page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

use std::env::args;
use std::process::exit;
use std::str::FromStr;

const LIMIT: i32 = 93;

fn usage() -> ! {
    println!("Usage: please input the count of fibonacci numbers to output");

fn parse_int<T: FromStr>(s: &str) -> Result<T, <T as FromStr>::Err> {

fn fibonacci(terms: i32) {
    if terms > LIMIT {
        println!("The number of terms you want to calculate is too big!");
        println!("The limit is {}.", LIMIT);
    } else {
        let mut a = 0u64;
        let mut b = 1u64;
        for i in 1..(terms + 1) {
            (a, b) = (b, a + b);
            println!("{i}: {a}");

fn main() {
    let mut args = args().skip(1);

    // Exit if 1st command-line argument not an integer
    let mut input_num: i32 = args
        .and_then(|s| parse_int(&s).ok())
        .unwrap_or_else(|| usage());

    // Show request number of Fibonacci numbers

Fibonacci in Rust was written by:

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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How to Run the Solution

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