Got sick of not having a calculator that can solve quadratics, so I made one. In Rust!

solve_quadratic.rs

use std::{error::Error, io::{self, prelude::*}};

fn main() -> Result<(), Box<dyn Error>> {
    let variable = std::env::args().nth(1).unwrap_or("x".into());
    let a = read_f64("A: ")?;
    let b = read_f64("B: ")?;
    let c = read_f64("C: ")?;
    let descriminent = descrim(a, b, c);
    let pos = pos_solution(a, b, descriminent);
    let neg = neg_solution(a, b, descriminent);
    let desc_string = format!("\\sqrt{{{}^2-4\\times {}\\times {}}}", b, a, c);
    println!("\n${}x^2{:+}x{:+} = 0$:", a, b, c);
    println!("Descriminent:\t${} = {}$", desc_string, descriminent);
    println!("Pos Solution:\t$\\frac{{{}+{}}}{{2\\times {}}} = {}$", b, desc_string, a, pos);
    println!("Neg Solution:\t$\\frac{{{}-{}}}{{2\\times {}}} = {}$", b, desc_string, a, neg);
    println!("$({0}{1:+})({0}{2:+}) = 0$", variable, neg, pos);
    println!("${0} = {1}$ or ${0} = {2}$", variable, -pos, -neg);
    Ok(())
}

fn read_f64(prompt: &str) -> io::Result<f64> {
        let mut buf = String::new();
    loop {
        buf.clear();
        print!("{}", prompt);
        io::stdout().flush()?;
        io::stdin().read_line(&mut buf)?;
        match buf.trim().parse() {
            Ok(val) => return Ok(val),
            Err(e) => {
                eprintln!("{}", e);
                continue
            },
        }
    }
}

fn descrim(a: f64, b: f64, c: f64) -> f64 {
    ((b*b) - (4.0*a*c)).sqrt()
}

fn pos_solution(a: f64, b: f64, desc: f64) -> f64 {
    (b+desc) / (2.0*a)
}

fn neg_solution(a: f64, b: f64, desc: f64) -> f64 {
    (b-desc) / (2.0*a)
}