count the number of times "5" appears when counting from 1 to 1000

fives.rs

fn main() {
    let mut c = 0;
    for i in 1..=1000 {
        let mut j = i;
        while j > 0 {
            if j % 10 == 5 {
                c += 1;
            }
            j /= 10;
        }
    }
    println!("{}", c);
}