Roman Numeral

Published on 07 October 2018 (Updated: 22 January 2024)

Welcome to the Roman Numeral page! Here, you'll find a description of the project as well as a list of sample programs written in various languages.

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Roman numerals are the numbers that were used in ancient Rome, which employed combinations of letters from the Latin alphabet (I, V, X, L, C, D and M).

The following table shows the letter to decimal mapping:

Letter Decimal
I 1
V 5
X 10
L 50
C 100
D 500
M 1000

Stringing together these digits yields a value that is the sum of their respective mappings. However, there is a catch. Roman numerals must appears in order of greatest to least. If a smaller value appears before a larger one, the smaller value is subtracted from the total.

As a result, a string like XV would evaluate to 15 while XIV would evaluate to 14.

Of course, there are other limitations, but we'll ignore those for simplicity.


Create a file called Roman Numeral Conversion using whatever naming convention is appropriate for the choice language.

Using the table above, write a sample program which accepts a Roman numeral on the command line and outputs its decimal value on standard output. Be careful to appropriately handle invalid input such as XT. More on that in the testing section.

Please make sure your program is executable. In other words, the solution should be able to be called in the appropriate environment with a string of roman numerals (i.e. ./roman-numeral-conversion XXVI).


Every project in the Sample Programs repo should be tested. In this section, we specify the set of tests specific to Roman Numeral. In order to keep things simple, we split up the testing as follows:

Roman Numeral Valid Tests

Description Input Output
Empty Input "" "0"
Single I "I" "1"
Single V "V" "5"
Single X "X" "10"
Single L "L" "50"
Single C "C" "100"
Single D "D" "500"
Single M "M" "1000"
Addition "XXV" "25"
Subtraction "XIV" "14"

Roman Numeral Invalid Tests

Description Input Output
No Input   "Usage: please provide a string of roman numerals"
Invalid Input "XT" "Error: invalid string of roman numerals"