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Roman Numeral to Decimal Converter

Explic1t (7)
I am trying to make a program that converts roman numerals to decimal form by adding and subtracting. EX: LX = 60. I would like to know if im doing this right and if what mistakes I may have made. If anyone can help it would be greatly appreciated.

This is my header file.
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#include <iostream>

using namespace std;

class romanNO
{
public:
		void get();
		void show();	
		romanNO(char&);
		int convert();
		int length();


private:
	int M,D,C,L,X,V,I;
	char romanNum;
	
		
	
};


This my main file.
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#include <iostream>
#include "roman.h"
#include <string>

using namespace std;

int main()
{
	char romanNum;

	cout << "Welcome to the Roman Numeral Converter. Please enter the number you would like to convert: ";
	cin >> romanNum;

	int sum = 0;

	int i;
	int length;

	int previous = 1000;

	for(i = 0; i < length; i++)
	{
		switch(romanNO[i])
		{
		case 'M':
			sum += 1000;
			if(previous < 1000)
			{
				sum -= 2 * previous;
			}
			previous = 1000;
			break;
		case 'D':
			sum += 500;
			if(previous < 500)
			{
				sum -= 2 * previous;
			}
			previous = 500;
			break;
		case 'C':
			sum += 100;
			if(previous < 100)
			{
				sum -= 2 * previous;
			}
			previous = 100;
			break;
		case 'L':
			sum += 50;
			if(previous < 50)
			{
				sum -= 2 * previous;
			}
			previous = 50;
			break;
		case 'X':
			sum += 10;
			if(previous < 10)
			{
				sum -= 2 * previous;
			}
			previous = 10;
			break;
		case 'V':
			sum += 5;
			if(previous < 5)
			{
				sum -= 2 * previous;
			}
			previous = 5;
			break;
		case 'I':
			sum += 1;
			if(previous < 1)
			{
				sum -= 2 * previous;
			}
			previous = 1;
			break;
		}
		return 0;
	}

	romanNO roman = romanNO(romanNum);
	cout << roman.convert() << endl;

	system("pause");

	return 0;
}



This is my .cpp file.
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#include <iostream>
#include "roman.h"

using namespace std;

romanNO::romanNO(char& ch)
{
	M = 1000;
	D = 500;
	C = 100;
	L = 50;
	X = 10;
	V = 5;
	I = 1;
	cout << ch << endl;
	romanNum = ch;
}

int romanNO::convert()
{
	/*if(romanNum == 'M')
	{
		return 1000;
	}
	else if(romanNum == 'D')
	{
		return 500;
	}
	else if(romanNum == 'C')
	{
		return 100;
	}
	else if(romanNum == 'L')
	{
		return 50;
	}
	else if(romanNum == 'X')
	{
		return 10;
	}
	else if(romanNum == 'V')
	{
		return 5;
	}
	else if(romanNum == 'I')
	{
		return 1;
	}*/
	return 0;
	
}

void romanNO::show()
{
	cout << romanNum << endl;
}

void romanNO::get()
{
}
Azagaros (410)
looks like you are doing cpp, this is using all your code you already had with a minor change.

So I will suggest this:
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#include <iostream>
#include <string>

using namespace std;

class RomanNumber
{
public:
		string get() {return RomanNumber;}

		void show()
                {
                       cout << "Roman Number is " << romanNumber << endl;
                }
                

		RomanNumber(const string &input);
                {
                       romanNumber = input;
                }

		int convert();
                {
                      int length = romanNumber.length();
                      int previous = 0;
                      bool error = false;
                      int nIndex = 0;

                      sum = 0;

                      while( (error == false) && (nIndex < length) )
	              {
		            switch(romanNumber[nIndex])
		            {
		                  case 'M':
			                sum += 1000;
			                if(previous < 1000)
			                {
				            sum -= 2 * previous;
			                }
			                previous = 1000;
			                break;
		                case 'D':
			                sum += 500;
			                if(previous < 500)
			                {
				             sum -= 2 * previous;
			                }
			                previous = 500;
			                break;
		                case 'C':
			                sum += 100;
			                if(previous < 100)
			                {
				              sum -= 2 * previous;
			                }
			                previous = 100;
			                break;
		               case 'L':
			                sum += 50;
			                if(previous < 50)
			                {
				             sum -= 2 * previous;
			                }
			                previous = 50;
			                break;
		               case 'X':
			                sum += 10;
			                if(previous < 10)
			                {
				              sum -= 2 * previous;
			                }
			                previous = 10;
			                break;
		               case 'V':
			                sum += 5;
			                if(previous < 5)
			                {
				             sum -= 2 * previous;
			                }
			                previous = 5;
			                break;
		               case 'I':
			                sum += 1;
			                if(previous < 1)
			                {
				              sum -= 2 * previous;
			                }
			                previous = 1;
			                break;
                               default:
                                        cout << romanNumber[nIndex] << " is not a Roman Numeral!" << endl;
                                        error = true;
                                        sum = 0;
		               } // switch

                               nIndex++;

                      } // while 
                      return sum;
	        }

		int length() {return romanNumber.length();}

private:
        string romanNumber;
        int sum;		
};

int main()
{
       string myInput = "LX";

       RomanNumber myRomanNumber(myInput);
       int value = myRomanNumber.convert();
       
       cout << "Roman Number " << myInput << " equals " << value <<endl;
}


Hope this points you in a direction.

If you can't use string of the Standard library, you could replace with char romanNumber[30] which is a string of characters with a length of 30.
whitenite1 (1785)
As the program is right now, you'll still get a few errors. You need to remove the semi-colons on lines 17 and 22
Explic1t (7)
@Azagaros The code works fine but I was looking more towards the user inputing the Roman Numbers and output what that roman number equals. EX: XXLVI = 56. You have it where the program already has is the input. Is there a way to change it to have the user input the roman numbers?
Last edited on
whitenite1 (1785)
@Explicit
Here is the program that allows for user input.
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// Roman Numerals To Decimal.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"  // Used because I compile with MS Visual C++ 2008, and this is needed for it
#include <iostream>
#include <string>

using namespace std;

 struct RomanNumber
{
public:
	string get()
	{
		return romanNumber;
	}

	void show()
	{
		cout << "Roman Number is " << romanNumber << endl;
	}

	RomanNumber(const string &input)
	{
		romanNumber = input;
	}

	int convert()
	{
		int length = romanNumber.length();
		int previous = 0;
		bool error = false;
		int nIndex = 0;

		sum = 0;

		while( (error == false) && (nIndex < length) )
		{
			switch(romanNumber[nIndex])
			{
			case 'M':
				sum += 1000;
				if(previous < 1000)
				{
					sum -= 2 * previous;
				}
				previous = 1000;
				break;
			case 'D':
				sum += 500;
				if(previous < 500)
				{
					sum -= 2 * previous;
				}
				previous = 500;
				break;
			case 'C':
				sum += 100;
				if(previous < 100)
				{
					sum -= 2 * previous;
				}
				previous = 100;
				break;
			case 'L':
				sum += 50;
				if(previous < 50)
				{
					sum -= 2 * previous;
				}
				previous = 50;
				break;
			case 'X':
				sum += 10;
				if(previous < 10)
				{
					sum -= 2 * previous;
				}
				previous = 10;
				break;
			case 'V':
				sum += 5;
				if(previous < 5)
				{
					sum -= 2 * previous;
				}
				previous = 5;
				break;
			case 'I':
				sum += 1;
				if(previous < 1)
				{
					sum -= 2 * previous;
				}
				previous = 1;
				break;
			default:
				cout << romanNumber[nIndex] << " is not a Roman Numeral!" << endl;
				error = true;
				sum = 0;
			} // switch

			nIndex++;

		} // while 
		return sum;
	}

	int length() 
	{
		return romanNumber.length();
	}

private:
	string romanNumber;
	int sum;		
};

int main()
{
	string myInput;
	int value;
	cout << "Please enter the Roman Numeral to convert : ";
	cin >> myInput;
	RomanNumber myRomanNumber(myInput);
	value = myRomanNumber.convert();
	
	cout << "Roman Number " << myInput << " equals " << value <<endl;
	
}

mzimmers (578)
I'm not sure how much this matters, but...something like "XXLVI" is not a valid Roman numeral. That value should be expressed "XXXVI."

How strictly you want to adhere to proper Roman numerology will influence your parsing rules.
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