# Roman Numeral Conversion in Every Language

Published on 01 November 2018 (Updated: 02 May 2020)

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.

## Requirements

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`

).

## Testing

The following table contains appropriate examples for testing a Roman Numeral Conversion program:

Description | Input | Output |
---|---|---|

No Input | “Usage: please provide a string of roman numerals” | |

Invalid Input | “XT” | “Error: invalid string of roman numerals” |

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 |

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## Further Reading

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