Class Functions Not Working

I am taking a Data Structures using C++ class. This is my second program for this class, and I just finished 46 programs in my C++ class.

The chapter covered Classes, the basics only.
The program is to convert the roman number into an Arabic (decimal) number.
The progam consists of a class.
That should:
-Store the number as a roman numeral.
-Convert and store the number as a decimal.
-Print the number as a roman or decimal number as requested by the user.
And there are three roman numerals to test the code.

Everything I here compiles, but doesn't give the right result. I only get one roman numeral character to print and the arabic equivalent is the first two characters plus the previous amount.

I have gone cross-eyed looking at this, and can't see what the problem might be.

I would appreciate a few more peepers to take a look.

My "romanType.h" file

Code:

#include <string>
using namespace std;

class romanType
{
public:
	romanType();
	//Default Constructor

	romanType(string roman);
	//Constructor

	void storeRomanNumber(string roman);
	//Function to store the roman numeral
	//Checks to see if all characters in the string are valid

	void convertRomanNumber();
	//Function to convert the Roman Number into and equivalent Arabic Number

	void printRomanNumber();
	//Prints the Roman Number as entered by the user

	void printArabicNumber();
	//Prints the converted Arabic equivalent number
	
private:
	int romanToArabic;
	string romanNumeral;
};

My romanType.cpp" file - with the function definitions for my class

Code:

#include "romanType.h"

romanType::romanType()
{
    romanNumeral = 'O';
    romanToArabic = 0;
}

romanType::romanType(string roman)
{
    storeRomanNumber(roman);
}

void romanType::storeRomanNumber(string roman)
{
	for (int i = 0; i < roman.size(); i++)
		if (islower(roman[i]))
			roman[i] = toupper(roman[i]);

	for (int i = 0; i < roman.size(); i++)
	{
		if (roman[i] == 'M' ||
			roman[i] == 'D' ||
			roman[i] == 'C' ||
			roman[i] == 'L' ||
			roman[i] == 'X' ||
			roman[i] == 'V' ||
			roman[i] == 'I')
			romanNumeral[i] = roman[i];
		else
			romanNumeral[i] = 'N';
	}

}// end storeRomanNumber

void romanType::convertRomanNumber()
{
	int a = 0,
	     z = 0,
	     minusMaybe = 0;
	for (int i = romanNumeral.size(); i >= 0; i--)
	{
		if (romanNumeral[i] == 'M') z = 1000;
		if (romanNumeral[i] == 'D') z = 500;
		if (romanNumeral[i] == 'C') z = 100;
		if (romanNumeral[i] == 'L') z = 50;
		if (romanNumeral[i] == 'X') z = 10;
		if (romanNumeral[i] == 'V') z = 5;
		if (romanNumeral[i] == 'I') z = 1;

		if (z < a) minusMaybe = -1;
		else minusMaybe = 1;

		romanToArabic = romanToArabic + (z * minusMaybe);
		a = z;
	}// end for
}// end convertRomanNumber

void romanType::printRomanNumber()
{
	cout << romanNumeral << endl;
}

void romanType::printArabicNumber()
{
	cout << romanToArabic << endl;
}

and, finally my "romanNumeralMain.cpp" file

Code:

#include <iostream>
#include <string>
#include "romanType.h"

using namespace std;

void displayBanner();
void displayQuestion();

int main()
{
	romanType romanNum;

	char userSelection;
	string roman;

	displayBanner();
	
	romanNum.storeRomanNumber("mcxiv");
	romanNum.convertRomanNumber();
	cout << "\nThe Roman numeral: ";
	romanNum.printRomanNumber();
	cout << "is equivalent to: ";
                romanNum.printArabicNumber();
	cout << endl;

	romanNum.storeRomanNumber("ccclix");
	romanNum.convertRomanNumber();
	cout << "\nThe Roman numeral: ";
	romanNum.printRomanNumber();
	cout << "is equivalent to: ";
                romanNum.printArabicNumber();
	cout << endl;

	romanNum.storeRomanNumber("MDCLXVI");
	romanNum.convertRomanNumber();
	cout << "\nThe Roman numeral: ";
	romanNum.printRomanNumber();
	cout << "is equivalent to: ";
                romanNum.printArabicNumber();
	cout << endl;

	displayQuestion();
	cin >> userSelection;

	while (userSelection == 'Y' || userSelection == 'y')
	{
		cout << "\nEnter a Roman numeral: ";
		cin >> roman;
		cout << "\nThe Roman numeral you entered is: ";
		romanNum.printRomanNumber();
		romanNum.storeRomanNumber(roman);
		cout << "\nThe Arabic equivalent of this Roman numeral is: ";
		romanNum.convertRomanNumber();
		romanNum.printArabicNumber();
		cout << endl;

		displayQuestion();
		cin >> userSelection;
	}// end while
}// end main


void displayBanner()
{
	cout << "\nThis program allows you to enter a Roman numeral;"
	        << "\nit then converts the string of characters into"
	        << "\nthe equivalent Arabic number.\nHere are some examples:";
}

void displayQuestion()
{
	cout << "\nThe Roman to Arabic conversion is:"
                        << "\n\tM = 1000\n\tD = 500\n\tC = 100\n\tL = 50\n\tX = 10\n\tV = 5\n\tI = 1\n"
                        << "\nWould you like to enter a Roman numeral to convert?" << endl;
}

Thanks for the help if anyone can!

Thanks ALL!
But, I figured it out.