Fahrenheit <=> Celsius converter in Rust

Question

It's one of the tasks suggested in the Rust Programming Language book by Steve Klabnik and Carol Nichols, and to a complete Rust newbie like me, figuring out converting scale from String to Vec<char>, was a bit of a challenge and a new concept, coming from Python.

I'd appreciate constructive criticism of what I've done wrong and right, pitfalls I may have fallen into, and possible optimizations available to be introduced to my code below.

use std::io;

fn main() {
    println!("Please type `exit` to quit the program.");

    loop {
        println!("Please input source scale.\n`C` for Celsius, `F` for Fahrenheit.");

        let mut scale = String::new();

        io::stdin()
            .read_line(&mut scale)
            .expect("Failed to read input.");

        if scale.trim() == "exit" {
            break;
        }

        let scale = scale.trim().to_uppercase();

        let scale: Vec<char> = scale.chars().collect();

        let scale = scale[0];

        let scale = match scale {
            'C' => 'C',
            'F' => 'F',
            _ => {
                println!("Incorrect scale.");
                continue;
            }
        };

        println!("Please input your source temperature with a trailing dot.");

        let mut temperature = String::new();

        io::stdin()
            .read_line(&mut temperature)
            .expect("Failed to read input.");

        if temperature.trim() == "exit" {
            break;
        }

        let temperature: f64 = match temperature.trim().parse() {
            Ok(num) => num,
            Err(_) => {
                println!("Please input a valid temperature.");
                continue;
            }
        };

        println!(
            "Converted temperature is: {}.",
            convert_temperature(scale, temperature)
        );
    }
}

fn convert_temperature(scale: char, temperature: f64) -> f64 {
    let converted_temperature: f64 = if scale == 'F' {
        (temperature as f64 - 32.0) / 1.8
    } else {
        temperature as f64 * 1.8 + 32.0
    };

    return converted_temperature;
}

Answer 1

You don't need to convert the strings to characters. This will make things much simpler while handling text.

use std::io;

fn main() {
    println!("Please type `exit` to quit the program.");

    loop {
        println!("Please input source scale.\n`C` for Celsius, `F` for Fahrenheit.");

        let mut scale = String::new();

        io::stdin()
            .read_line(&mut scale)
            .expect("Failed to read input.");

        if scale.trim().to_lowercase() == "exit" {
            break;
        }

        let scale = scale.trim().to_uppercase();
        if scale.ne("C") && scale.ne("F") {
                println!("Incorrect scale.");
                continue;
        };

        println!("Please input your source temperature: ");

        let mut temperature = String::new();

        io::stdin()
            .read_line(&mut temperature)
            .expect("Failed to read input.");

        if temperature.trim().to_lowercase() == "exit" {
            break;
        }

        let temperature: f64 = match temperature.trim().parse() {
            Ok(num) => num,
            Err(_) => {
                println!("Please input a valid temperature.");
                continue;
            }
        };

        println!(
            "Converted temperature is: {}.",
            convert_temperature(scale, temperature)
        );
    }
}

fn convert_temperature(scale: String, temperature: f64) -> f64 {
    let converted_temperature: f64 = if scale == "F" {
        (temperature as f64 - 32.0) / 1.8
    } else {
        temperature as f64 * 1.8 + 32.0
    };

    return converted_temperature;
}

s1.ne(s2) is a string function that checks if s1 is not equal to s2.

There is also no need for asking for a dot at the end of the number to be entered by the user.