Programming Challenge - Rust - Roman Numerals Checkpoint 1

main.rs

use std::env;

fn main() {
    // get the command line argument
    let args: Vec<String> = env::args().collect();

    // first command line arg is the program
    if args.len() < 2 {
        panic!("must supply a command line argument of the number to convert");
    }

    // parse or fail
    let i = args[1].parse::<i32>().expect("Unable to parse command line argument to int");

    // compute the roman numeral
    let rn = make_roman_numeral(i);
    println!("made roman numeral for {:?} - {:?}", i, rn);
}

// associate a roman numeral with its value
struct RomanNumeral {
    txt: char,
    value: i32,
}

fn get_roman_numerals_descending() -> Vec<RomanNumeral> {
    vec![
        RomanNumeral {txt: 'M',value: 1000},
        RomanNumeral {txt: 'D',value: 500},
        RomanNumeral {txt: 'C',value: 100},
        RomanNumeral {txt: 'L',value: 50},
        RomanNumeral {txt: 'X',value: 10},
        RomanNumeral {txt: 'V',value: 5},
        RomanNumeral {txt: 'I',value: 1},
    ]
}

fn make_roman_numeral(i: i32) -> String {
    let descending = get_roman_numerals_descending();
    let mut roman_numeral = String::new();
    let mut remainder = i;

    // find the largest roman numeral smaller than remainder,
    // append the roman character, and deduct from the remainder
    while remainder > 0 {
        if remainder == 0 {
            break;
        }

        for rn in &descending {
            if rn.value <= remainder {
                roman_numeral.push(rn.txt);
                remainder -= rn.value;
                break;
            }
        }
    }

    roman_numeral
}