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Lee's Roman Numeral Converter
by Lee K. Seitz

Frequently Asked Questions

What do the letters stand for?

Why doesn't 1999 = MIM (or 99 = IC or 999 = IM or ... )?

How do Roman numerals work?

Can you send me the source code?

Why is there a limit of 3999?

Q: What do the letters stand for?
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000.

Q: Why doesn't 1999 = MIM (or 99 = IC or 999 = IM or ... )?
The rules for Roman numerals as I learned them include:

You can only subtract a power of ten from any Roman numeral.

You can only subtract from the next two higher "digits."

That is, you can only subtract I from V and X. You can only subtract X from L and C. And you can only subtract C from D and M. Or, in other words, subtraction is only done for (4 x 10n) and (9 x 10n). (That is, 4, 40, 400, 9, 90, and 900.)

Or, to put it a completely different way: When converting to Roman numerals, convert each digit separately. So for 999, convert 900, 90, and 9 to give CM, XC, and IX (CMXCIX). Note that the Romans themselves didn't necessarily follow these rules, but as with everything else in Western society, we created more rules for it as time passed.

Q: How do Roman numerals work?
That is a section unto itself.

Q: Can you send me the source code?
It seems writing an Arabic to Roman numeral converter is a fairly common assignment in beginning programming classes. I'm a firm believer in students doing their own work, so I will not give the source to anyone. But I have written a rather vague explanation of how the code works.

Q: Why is there a limit of 3999?
The highest "digit" available is M. Writing 4000 in Roman numerals would require subtracting 1000 (M) from 5000. There actually is a Roman numeral for 5000; it's V with a bar over it. Unfortunately, doing this notation in HTML is difficult at best, so I've simply limited the converter to 3999.


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