Roman Numerals Converter

Roman numerals represent numbers with combinations of seven capital letters: I, V, X, L, C, D, and M. Their basic values are 1, 5, 10, 50, 100, 500, and 1000. Unlike the modern decimal system, Roman notation has no place value and no symbol for zero. A number is usually formed by adding symbol values from left to right, but selected smaller symbols placed before larger symbols indicate subtraction. The standard subtractive pairs are IV for 4, IX for 9, XL for 40, XC for 90, CD for 400, and CM for 900. These pairs keep notation compact and canonical. For example, 1994 becomes MCMXCIV: M contributes 1000, CM contributes 900, XC contributes 90, and IV contributes 4. Writing the same value with unrestricted repetition may be understandable historically, but this converter accepts and produces the conventional modern form used in references, education, clocks, outlines, and publication dates. To convert an Arabic number to Roman notation, the algorithm works from the largest available value downward. It repeatedly appends the matching symbol and subtracts its value until the remainder reaches zero. Including subtractive pairs in the ordered value table ensures that 9 becomes IX rather than VIIII and 900 becomes CM rather than DCCCC. The supported range ends at 3999 because standard notation without overlines has a practical maximum of MMMCMXCIX. Conversion in the opposite direction also scans symbols from largest to smallest. The converter then regenerates the canonical Roman form and compares it with the entered text. This validation rejects malformed strings such as IIII, VX, or IIV even if a loose arithmetic parser could assign them a number. Input is case-insensitive, and surrounding spaces are ignored, but the displayed result follows the traditional uppercase convention. Roman numerals still appear on monuments, building cornerstones, film copyright screens, book chapters, sporting events, monarch names, and clock faces. Some decorative uses intentionally vary from canonical rules; for example, clocks often display four as IIII instead of IV for visual balance. This tool follows modern textbook notation, so those stylistic variants may be rejected. For historical inscriptions, remember that actual Roman practice changed across periods and was less standardized than the rules commonly taught today.