Project: Roman numeral converter

Overview

Teaching: 0 min
Exercises: 150 min

Questions

• Write a Roman numeral converter

Objectives

• Learn how to solve a problem by designing a Python program

• Get more hands-on experience

As our first programming exercise, we’ll build a Roman number converter. This will help you to go through the full process of designing a program to solve a data challenge.

Introduction to Roman Numerals

Roman numerals originated in ancient Rome and have been used throughout Western Europe until the late Middle Ages. They are composed of combinations of letters from the Latin alphabet: I, V, X, L, C, D, and M, which stand for:

• I = 1
• V = 5
• X = 10
• L = 50
• C = 100
• D = 500
• M = 1000

Basic Rules of Roman Numerals:

1. Addition: When a smaller numeral appears after a larger or equal one, you add the values (e.g., VI is 6 because V + I = 6).
2. Subtraction: When a smaller numeral appears before a larger one, you subtract the smaller from the larger (e.g., IV is 4 because I is before V). The most common subtraction combinations are:
   • I can be placed before V and X to make 4 and 9.
   • X can be placed before L and C to make 40 and 90.
   • C can be placed before D and M to make 400 and 900.
3. Repetition: The same symbol can be repeated up to three times in succession. For example:
   • III = 3
   • XXX = 30
4. Combination: Roman numerals are usually written from largest to smallest from left to right, apart from when doing subtractions.

Examples:

• III = 1 + 1 + 1 = 3
• IV = 5 - 1 = 4
• IX = 10 - 1 = 9
• LVIII = 50 + 5 + 3 = 58
• MCMXCIV = 1000 + (1000 - 100) + (100 - 10) + (5 - 1) = 1994

Why It Matters in Programming

Converting between Roman and Arabic numerals involves understanding both addition and subtraction rules, making it an excellent exercise for developing algorithms. You’ll need to read in strings of characters while adhering to specific logic patterns —- a fundamental skill in programming.

As you embark on this project, think about the different approaches you can take. Consider efficiency, readability, and how you might handle edge cases or errors (such as invalid numeral sequences). This will not only help you write better code but also enhance your problem-solving skills.

Bonus challenge

Write an Arabic to Roman numeral converter, e.g. going the other way around.

Key Points