Why won't this code work?

[_Kyjko]

I'm quite new to Rust, I wanted to write a really simple Caeser cipher which moves every letter forward by 1 in the alphabet, but I get this error, and I couldn't figure out the exact cause. I'd appreciate any suggestions about what I'm doing wrong.

use std::io;
fn main(){

    let letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    let mut buffer: Vec<char> = Vec::new();

    let mut s = String::new();

    io::stdin().read_line(&mut s)
    .expect("Cannot read input!");

    for _char in s.chars() {
        let index = letters.chars().position(|r| r == _char).unwrap();
        let new_index = index+1 % letters.len();

        buffer.push(letters.chars().nth(new_index).unwrap());
    }

    for _char in buffer.iter() {
        print!("{}", _char);
    }

}

Error: thread 'main' panicked at 'called Option::unwrap() on a None value'

[birkenfeld]

Your input string includes the newline character, which does not exist in letters.
Usually you would just "pass through" any characters that can't be encoded.

index+1 % letters.len() won't work properly either, since % binds more tightly than +.

[gipec]

Use something like: let s = s.trim(); after reading from stdin, and you must deal with lowercase, punctuation etc. Otherwise it will panick again.

[stevensonmt]

FWIW, treating chars as u8 might simplify this problem as well and keep you from needing that sort of reference string as a lookup table.

[Yandros]

Yes, something along these lines:

• Playground

[stevensonmt]

I love that. Tweaked it a bit to show using a type alias for u8 instead of a struct with a single field.

Rust Playground