Why does my string not match when reading user input from stdin?

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Instead of trim_end_matches (previously called trim_right_matches), I’d recommend using trim_end (previously called trim_right) or even better, just trim:

use std::io;

fn main() {
    let mut correct_name = String::new();
    io::stdin()
        .read_line(&mut correct_name)
        .expect("Failed to read line");

    let correct_name = correct_name.trim();

    if correct_name == "y" {
        println!("matched y!");
    } else if correct_name == "n" {
        println!("matched n!");
    }
}

This last case handles lots of types of whitespace:

Returns a string slice with leading and trailing whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space.

Windows / Linux / macOS shouldn’t matter.

You could also use the trimmed result’s length to truncate the original String, but in this case you should only use trim_end!

let trimmed_len = correct_name.trim_end().len();
correct_name.truncate(trimmed_len);

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