Learning rust - Convert temperatures between Fahrenheit and Celsius

I've just started going through the Rust-lang tutorial and I guess it is the first of many posts about learning rust (or maybe not).

My takeaways so far:

• if statements doesn't have parentehesises as in Go
• cargo is pretty neat tool
• when reading input from STDIN, don't forget to trim single trailing newline.

And as tutorial suggests, I've written temperature converter from Fahrenheit and Celsius and other way around:

use std::io;
use std::string::String;

fn main() {
    println!("Please, choose conversion type:");
    println!("[1] Fahrenheit to Celsius");
    println!("[2] Celsius to Fahrenheit");

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

    // trim single trailing newline.
    option.pop();

    if option != "1" && option != "2" {
        println!("Wrong input, please select 1 or 2.");
        return
    }

    println!("Please, type tempereture.");

    let mut tmp = String::new();

    io::stdin()
            .read_line(&mut tmp)
            .expect("Failed to read line");

    let tmp: i32 = match tmp.trim().parse() {
            Ok(num) => num,
            Err(_) => {
                println!("Can't parse input.");
                return
            },
        };

    if option == "1" {
        to_celsius(tmp);
    } else if option == "2" {
        to_fahrenheit(tmp);
    }
}

fn to_celsius(f :i32) {
    println!("{} C", (f - 32)*5/9);
}

fn to_fahrenheit(c :i32) {
    println!("{} F", c*9/5+32);
}