Converts a integer to a roman number.

int2roman-num.cpp

#include <iostream>
#include <array>
#include <string>
#include <map>

// This is free and unencumbered software released into the public domain.
// Anyone is free to copy, modify, publish, use, compile, sell, or
// distribute this software, either in source code form or as a compiled
// binary, for any purpose, commercial or non-commercial, and by any
// means.
// (see https://unlicense.org)
// ----

// @brief Converts a given integer to roman number
// (can be used with signed / unsigned integer)
// @param i [In] The number to convert.
// @returns std::string Resulting string.
template<typename TInt = int64_t>
std::string intToRomanNum(TInt i)
{
    static_assert(std::is_integral<TInt>::value, "[intToRomanNum] Type isn't an integer.");

    std::string result;
    
    // Check if number 0 (probably unneccesary to check if signed, just compare)
    // (this can probably be 'if constexpr' in c++17)
    if (std::is_signed<TInt>::value)
    {
        if (i == 0)
        {
            return std::string("0");
        }
        if (i < 0)
        {
            // append '-' to the target string and make given 'i' positive
            // Probably not a valid rule but a fail-safe (because the while loop runs mindlessly)
            result.append("-");
            i = -i;
        }
    }
    else
    {
        if (i == 0U)
        {
            return std::string("0");
        }
    }

    // Define a persistent scoped map variable
    static std::map<TInt, const char*> romNum;
    if (romNum.empty())
    {
        romNum =
        {
            { 1, "I" },
            { 4, "IV" },
            { 5, "V" },
            { 9, "IX" },
            { 10, "X" },
            { 40, "XL" },
            { 90, "XC" },
            { 100, "C" },
            { 400, "CD" },
            { 500, "D" },
            { 900, "CM" },
            { 1000, "M" }
        };
    }

    while (i > 0)
    {
        for (auto pair = romNum.rbegin(); pair != romNum.rend(); pair++)
        {
            while (i >= pair->first)
            {
                i -= pair->first;
                result.append(pair->second);
            }
        }
    }

    return result;
}

int main(int argc, const char *argv[])
{
    // Example program
    std::cout << "-- Convert Num --" << std::endl;

    int64_t a = 1;
    while (a != 0)
    {
        if (std::cin.bad())
        {
            std::cin.clear();
        }
    
        std::cin >> a;
        std::cout << "Number is : " << intToRomanNum(a) << std::endl;
    }
    
    return 0;
}