Factorial in Rust

Published on 31 October 2019 (Updated: 08 May 2023)

Welcome to the Factorial 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

//  Requirement     https://sample-programs.therenegadecoder.com/projects/factorial/
// Accept a number on command line and print it's factorial
// Works till factorial 34, which is 39 digits, ...
use std::env::args;
use std::process::exit;
use std::str::FromStr;

fn usage() -> ! {
    println!("Usage: please input a non-negative integer");

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

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

    // confirm positive integer is passed as command-line argument
    let mut input_num: u32 = args
        .and_then(|s| parse_int(&s).ok())
        .unwrap_or_else(|| usage());

    let mut n = input_num as u128;
    let mut result = 1;
    while n > 0 {
        result *= n;
        n -= 1;

Factorial in Rust was written by:

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

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.