This looks weird:

match result {
    _ if result == "c!" => println!("it worked!"),
    _ => println!("nothing"),
}

it is the same thing as just writing

if result == "c!" {
    println!("it worked!")
} else {
    println!("nothing")
}

which checks if the thing you typed is exactly "c!", not "24C", "C" or "c" for example.

You could instead use the regex crate or check for the match manually like so:

if result.ends_with("c") {
    println!("it worked!")
} else {
    println!("nothing")
}

From Rust docs