Decimal2Roman.java

import java.util.Scanner;   // for user input

public class Decimal2Roman {

    /**
    *   Program:    Decimal2Roman.java
    *   Purpose:    Convert decimal number to Roman numerals
    *   Creator:    Chris Clarke
    *   Created:    05.11.2012
    */

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        int decimal = 0;

        if (args.length > 0) {
            try {
                decimal = Integer.parseInt(args[0]);
            } catch (Exception e) {
                System.out.println("Not a whole number!");
                System.exit(1);
            } // end try/catch
        } else {
            System.out.print("Enter a whole number"
             +" for conversion to Roman: ");
            try {
                decimal = scan.nextInt();
            } catch (Exception e) {
                System.out.println("That\'s not a whole number!");
                System.exit(1);
            } // end try/catch
        } // end if/else

        System.out.println("In Roman numerals: "
         + getRomanNumerals( decimal));
    } // end main()

    public static String getRomanNumerals(int decimal) {

        String  ans="";

        if (decimal<0) {
            System.out.println("Postive numbers only!");
            return "Error";
        } else if (decimal>=4000) {
            System.out.println("Number too big"
            +" - must be less than 4000");
            return "Error";
        } // end if/else

        while (decimal>=1000) {
            ans += "M";
            decimal -= 1000;
        } // end while

        if (decimal>=900) {
            ans += "CM";
            decimal -= 900;
        } else if (decimal>=500) {
            ans += "D";
            decimal -= 500;
        } else if (decimal>=400) {
            ans += "CD";
            decimal -= 400;
        } // end if/else

        while (decimal>=100) {
            ans += "C";
            decimal -= 100;
        } // end while

        if (decimal>=90) {
            ans += "XC";
            decimal -= 90;
        } else if (decimal>=50) {
            ans += "L";
            decimal -= 50;
        } else if (decimal>=40) {
            ans += "XL";
            decimal -= 40;
        } // end if/else

        while (decimal>=10) {
            ans += "X";
            decimal -= 10;
        } // end while

        if (decimal==9) {
            ans += "IX";
            decimal -= 9;
        } else if (decimal>=5) {
            ans += "V";
            decimal -= 5;
        } else if (decimal==4) {
            ans += "IV";
            decimal -= 4;
        } // end if/else

        while (decimal>=1) {
            ans += "I";
            decimal--;
        } // end while

        return ans;

    } // end getRomanNumerals()
} // end class