Roman Numeral To Number Converter

RomanNumeralToNumber.cpp

#include "stdafx.h"
#include <string>
#include <iostream>
#include <map>

int romToNum(std::string rom);
bool ShouldSubtract(std::string rom, int position);

std::map<char, int> romNumMap;

int _tmain(int argc, _TCHAR* argv[])
{
	romNumMap['I'] = 1;
	romNumMap['V'] = 5;
	romNumMap['X'] = 10;
	romNumMap['L'] = 50;
	romNumMap['C'] = 100;
	romNumMap['D'] = 500;
	romNumMap['M'] = 1000;

	bool shouldContinue = true;
	while (shouldContinue)
	{
		std::cout << "Enter a valid roman numeral\n";
		std::string input;
		std::cin >> input;
		int converted = romToNum(input);
		std::cout << "Answer is: " << converted << "\n";
		std::cout << "Another? [y/n]\n";
		std::cin >> input;
		('y' == input[0]) ? shouldContinue = true : shouldContinue = false;
	}
	return 0;
}

int romToNum(std::string rom)
{
	int answer = 0;
	for (int y = 0; y < rom.size(); y++) 
	{
		ShouldSubtract(rom, y) ? answer -= romNumMap[rom[y]] : answer += romNumMap[rom[y]];
	}
	return answer;
}

bool ShouldSubtract(std::string rom, int position)
{
	if (position+1 > rom.size())
		return false;

	return (romNumMap[rom[position]] < romNumMap[rom[position+1]]) ? true : false;
}