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

read_line includes the terminating newline in the returned string. Add .trim_right_matches("\r\n") to your definition of correct_name to remove the terminating newline.

read_line includes the terminating newline in the returned string. To remove it, use trim_end 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);

You can use the chomp-nl crate which provides a chomp function which returns a string slice without the newline characters.

There is also a trait ChompInPlace if you prefer to do this in-place.

Disclaimer: I am the author of this library.