Print a new number by adding one to each of its digit

// https://www.reddit.com/r/dailyprogrammer/comments/aphavc/20190211_challenge_375_easy_print_a_new_number_by/

/**
#include <ctype.h>
#include <stdio.h>

int
main(void)
{
    int c;
    while (isdigit(c = getchar())) {
        int n = c - '0' + 1;
        if (n == 10)
            putchar('1');
        putchar('0' + n % 10);
    }
    putchar('\n');
}
*/

use std::{
    fs::File,
    io::{BufReader, BufWriter, Read, Write},
    os::unix::io::{FromRawFd, IntoRawFd},
};

fn main() {
    // https://www.reddit.com/r/rust/comments/9xedap/how_to_achieve_fast_stdinstdout_io_suitable_for/e9t4vle/
    let stdin = unsafe { File::from_raw_fd(0) };
    let stdout = unsafe { File::from_raw_fd(1) };
    let (mut reader, mut writer) = (BufReader::new(stdin), BufWriter::new(stdout));

    for byte in reader.by_ref().bytes() {
        let byte = byte.unwrap();
        if byte < b'0' || byte > b'9' {
            break;
        }

        let mut value = (byte - b'0') + 1;

        if value >= 10 {
            writer.write(&[b'1']).unwrap();
            value -= 10;
        }

        writer.write(&[value + b'0']).unwrap();
    }
    writer.write(&[b'\n']).unwrap();

    let _ = reader.into_inner().into_raw_fd();
    let _ = writer.into_inner().unwrap().into_raw_fd();
}