a simple Roman number calculator. It is to read a Roman number, an operator (+, -, /, or *), and a second Roman number. It then shows the calculation using Arabic numbers and prints the result as a Roman number.

Roman_Converter.rb

#!/usr/bin/env ruby

# AUTHOR: Mark Feltner

OPERANDS = {
    "I" => 1,
    "V" => 5,
    "X" => 10,
    "L" => 50,
    "C" => 100,
    "D" => 500,
    "M" => 1000
}

def to_arabic(roman_int)
    value = 0
    roman_int.chars { |c| value+=OPERANDS[c] }
    return value
end

def to_roman(arabic_int)
    roman_str = ""
    if arabic_int < 0
        arabic_int = arabic_int.abs
        roman_str += '-'
    elsif arabic_int == 0
        return "zero"
    end
    for k,v in OPERANDS.invert.sort.reverse
        if (x = arabic_int / k)>0 
            arabic_int = arabic_int % k 
            roman_str += OPERANDS.invert[k] * x
        end
    end
    return roman_str
end

def process_expression
    n = 1
    while (line = gets)
        expression = line.split " " 
        operand1 = to_arabic(expression[0])
        operand2 = to_arabic(expression[2])
        operator = expression[1]
        arabic_result = 0
        if operator == '+'
            arabic_result = operand1 + operand2
        elsif operator == '-'
            arabic_result = operand1 - operand2
        elsif operator == '*'
            arabic_result = operand1 * operand2
        elsif operator == '/'
            arabic_result = operand1 / operand2
        end
        roman_result = to_roman(arabic_result)
        puts "#{operand1} #{operator} #{operand2} = #{arabic_result} = #{roman_result}"
    end
end

process_expression