rust-book/ftoctof/src/main.rs


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use std::env;

fn print_usage() {
    eprintln!("error: usage: ftoctof [degrees] [f|c]");
}

fn main() {
    // grab degrees value
    let degrees: f32 = match env::args().nth(1) {
        Some(s) => {
            let attempt: f32 = s.trim().parse()
                .expect("error: could not parse degrees");
            attempt
        },
        None => {
            print_usage();
            return;
        },
    };

    // grab scale identifier
    let scale = match env::args().nth(2) {
        Some(s) => s.to_lowercase(),
        None => {
            print_usage();
            return;
        },
    };

    // compute and print conversion
    if scale == "f" {
        let result: f32 = (degrees - 32.0) * 5.0 / 9.0;
        println!("{} degrees fahrenheight is {} degrees celcius.", degrees, result);
    }
    else if scale == "c" {
        let result: f32 = degrees * 9.0 / 5.0 + 32.0;
        println!("{} degrees celcius is {} degrees fahrenheight.", degrees, result);
    }
    else {
        print_usage();
    }

}