praxis-rust/nines_and_zeros.rs

use std::env;

fn main() {
    if env::args().len() != 2 {
       println!("Usage: {} divisor", env::args().nth(0).unwrap());
       return;
    }

    let divisor = env::args().nth(1).unwrap().parse::<u64>().ok().expect("Input is not a number");

    let mut num: u64 = 0;
    let mut s: u64 = 9;
    while s % divisor != 0 {
        num += 1;
        s = format!("{:b}", num).replace("1", "9").parse::<u64>().unwrap();
    }

    println!("Found: {}", s);
}