How to Convert Roman Numerals to Int While Rejecting Invalid Numbers Using Standard C?

Error Overview

The error message “How to convert Roman numerals to int while rejecting invalid numbers using standard C?” often arises when developers attempt to convert Roman numeral strings into their integer equivalents without adequately handling invalid inputs. Roman numerals are a numeral system originating from ancient Rome, and converting them correctly requires a clear understanding of both the values and the rules governing their construction. This article will guide you through the process of implementing a solution in C, providing robust handling for invalid numeral inputs.

Common Causes

Several common pitfalls can lead to errors during the conversion of Roman numerals to integers, including:

1. Invalid Roman Numerals: Inputs such as “IIII” or “VV” are not valid.
2. Incorrect Order: Roman numerals must be ordered correctly (e.g., “IX” for 9, not “XI” for 12).
3. Repetition Rules: Certain numerals can only be repeated a specified number of times (e.g., “I” appears at most 3 times).
4. Subtractive Notation: Misunderstanding how subtractive combinations work (e.g., “IV” must be treated as 4).
5. Overflow Handling: The conversion may result in integer overflow if the total exceeds the maximum value representable by an integer type.

Solution Methods

To address the issue effectively, we will explore three methods for converting Roman numerals to integers while rejecting invalid numbers.

Method 1: Using a Lookup Table

This method employs a static lookup table that maps valid Roman numeral components to their integer values. It uses a function to parse the string and validate the input.

1. Define the Lookup Table:
   “`c
   #include
   #include
   #include

struct Roman_digit