Roman Numeral Converter in C++

This program converts numbers to Roman numerals and vice versa. It is implemented in C++ and includes detailed explanations and documentation for clarity.

Program Structure

The program consists of the following components:

• romanToInt: Converts a Roman numeral string to an integer.
• intToRoman: Converts an integer to a Roman numeral string.
• main: Entry point of the program where conversion functions are demonstrated.

C++ Code

// RomanNumeralConverter.cpp
#include <iostream>
#include <string>
#include <unordered_map>

using namespace std;

/**
 * Function to convert Roman numeral to integer.
 * @param s: Roman numeral string.
 * @return Integer representation of the Roman numeral.
 */
int romanToInt(const string &s) {
    unordered_map<char, int> roman = {{'I', 1}, {'V', 5}, {'X', 10}, {'L', 50}, {'C', 100}, {'D', 500}, {'M', 1000}};
    int total = 0;
    int prevValue = 0;

    for (const char &c : s) {
        int currValue = roman[c];
        if (currValue > prevValue) {
            total += currValue - 2 * prevValue;
        } else {
            total += currValue;
        }
        prevValue = currValue;
    }

    return total;
}

/**
 * Function to convert integer to Roman numeral.
 * @param num: Integer value.
 * @return Roman numeral representation of the integer.
 */
string intToRoman(int num) {
    pair<int, string> valueSymbols[] = {
        {1000, "M"}, {900, "CM"}, {500, "D"}, {400, "CD"},
        {100, "C"}, {90, "XC"}, {50, "L"}, {40, "XL"},
        {10, "X"}, {9, "IX"}, {5, "V"}, {4, "IV"}, {1, "I"}
    };
    
    string result;
    for (const auto &pair : valueSymbols) {
        while (num >= pair.first) {
            result += pair.second;
            num -= pair.first;
        }
    }

    return result;
}

int main() {
    // Examples of conversion
    string romanNumeral = "MCMXCIV";
    int number = 1994;

    cout << "Roman numeral " << romanNumeral << " is " << romanToInt(romanNumeral) << " in integer." << endl;
    cout << "Integer " << number << " is " << intToRoman(number) << " in Roman numeral." << endl;

    return 0;
}

Explanation

The program contains two main functions: romanToInt and intToRoman.

romanToInt Function

• Uses an unordered map to store the Roman numeral characters and their corresponding integer values.
• Iterates through the input string and computes the integer value by checking if the current Roman numeral is greater than the previous one.
• If the current numeral is greater, it subtracts twice the previous value (since it was added once before) and adds the current value.
• Otherwise, it adds the current value directly to the total.

intToRoman Function

• Uses an array of pairs to store integer values and their corresponding Roman numeral strings, sorted from largest to smallest.
• Iterates through the array and appends the Roman numeral string to the result while subtracting the integer value from the number until the number becomes zero.

main Function

• Demonstrates the conversion by converting a Roman numeral string to an integer and an integer to a Roman numeral string.
• Outputs the results to the console.