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Roman Numerals Math?????

j123t (10)
I have to create a program that counts roman numerals. I'm not sure how I would do the math in it? I know if the smallest number is in front, you minus them... but I don't know how I would write that? Here is my code so far :

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#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

class romanType
{
      string numerals;
      int convert();
      void print();
};

void count();
      void displays();
string a, b;
int total = 0;

int main(int argc, char *argv[])
{
     ifstream deletefile ("romannums.out", ios::out | ios::trunc);     
deletefile.close();
     
    ifstream inFile;
    ofstream outFile;
    
    inFile.open("romannum.txt", ios::in);    
    outFile.open("romannums.out", ios::app); 
    
    int m = 1000;
    int d = 500;
    int c = 100;
    int l = 50;
    int x = 10;
    int v = 5;
    int i = 1;
    int number;
    string num;
    
    cout << "How many roman numerals do you have? : ";
    cin >> number;
    
for(int j=0; number > j; j++)
    {
    cout << "What is the letter?: " ;
    cin >> b;
    
    outFile << b;
    
    count();
    
    if(b<num)
    {cout << "hi" << endl;}
    num = b;
    } 
    
    outFile << endl;
    
    cout << endl;
    cout << "The total decimal value is : " << total << endl;
    cout << "The roman numeral is : ";
    displays();
    
    outFile.close();
    inFile.close();
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

void count()
{
     if(a=="M" || b == "M")
     {
     total=total+1000;
     }
     
     if(a=="D" || b == "D")
     {
     total=total+500;
     } 
     
     if(a=="C" || b == "C")
     {
     total=total+100;
     }
     
     if(a=="L" || b == "L")
     {
     total=total+50;
     }
     
     if(a=="X" || b == "X")
     {
     total=total+10;
     }
     
     if(a=="V" || b == "V")
     {
     total=total+5;
     }
     
     if(a=="I" || b == "I")
     {
     total=total+1;
     }
}

void displays() // Function to display data in customer order file
{
  string line;
  ifstream displayfile ("romannums.out");
  if (displayfile.is_open())
{while (displayfile.good())
    {
    getline (displayfile,line);
    cout << line << endl;
    }
displayfile.close();}

cout << '\n'; 
}
Shinigami (309)
Your code is incorrect. Here are not anything to fix.

You need to analyze the entire line of roman numbers in string.

How to do:
http://en.wikipedia.org/wiki/Roman_numerals
Last edited on
j123t (10)
I'm not sure how to do that.
Stewbond (2827)
Step 1:
Get a user input, (you've done that)
std::string roman = "MMXII";

Step 2:
Convert it to an integer (You need to define this function)
int num = RomanToInt(roman);

Step 3:
do the math with int num

Step 4:
Convert it back to roman numerals (You need to define this function too)
std::string roman_out = IntToRoman(num);
Stewbond (2827)
******SPOILER******

Here's a function that will turn a roman numeral string to an int. If I feel like it tonight I may try and write one that converts an int back to a roman numeral string.

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int RomanCharToInt(char in)
{	// Converts a single roman character to an integer
	if(in <0x60) in += 0x20; // Converts to lower-case (if applicable)
	switch (in)
	{
	case 'm':  return 1000;
	case 'd':  return 500;
	case 'c':  return 100;
	case 'l':  return 50;
	case 'x':  return 10;
	case 'v':  return 5;
	case 'i':  return 1;
	}
	return -9999999; // Very obscure number so the user knows there was a problem.
}

int RomanToInt(std::string &in)
{ // Converts a whole string of roman numerals to an integer
	int number = 0;
	int i = in.size()-1;
	
	// Get the first one
	number += RomanCharToInt(in[i--]);
	
	//Now loop for the rest
	while ( i > -1)
		if (RomanCharToInt(in[i]) < RomanCharToInt(in[i+1]))
			number -= RomanCharToInt(in[i--]);  // If it's less than the one before, subtract the value
		else 
			number += RomanCharToInt(in[i--]);  // else add the value	
	
	return number;
}
Last edited on
Shinigami (309)
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#include <iostream>
#include <string>
using namespace std;

class RomanDecimal {
	public:
		RomanDecimal(): roman_number(""), decimal_number(0), count_dec(1) {};
		~RomanDecimal();
		void add_roman(string);
		void add_decimal(int);
		string get_roman();
		int get_decimal();
		
	private:
		string roman_number;
		int decimal_number;
		void convert_to_roman();
		void convert_to_decimal();
		int count_dec;
		static const int i = 1;
		static const int v = 5;
		static const int x = 10;
		static const int l = 50;
		static const int c = 100;
		static const int d = 500;
		static const int m = 1000;
};

RomanDecimal::~RomanDecimal() {}

void RomanDecimal::add_roman(string number) {
	roman_number = number;
	convert_to_decimal();
}

void RomanDecimal::add_decimal(int number) {
	decimal_number = number;
	convert_to_roman();
}

void RomanDecimal::convert_to_decimal() {
	size_t length;
	
	length = roman_number.length();
	int * array_of_numbers = new int[length];
	
	for (unsigned int n = 0; n < length; n++){
		if (roman_number[n] == 'i' or roman_number[n] == 'I') {
			array_of_numbers[n] = i;
		}
		else if (roman_number[n] == 'v' or roman_number[n] == 'V') {
			array_of_numbers[n] = v;
		}
		else if (roman_number[n] == 'x' or roman_number[n] == 'X') {
			array_of_numbers[n] = x;
		}
		else if (roman_number[n] == 'l' or roman_number[n] == 'L') {
			array_of_numbers[n] = l;
		}
		else if (roman_number[n] == 'c' or roman_number[n] == 'C') {
			array_of_numbers[n] = c;
		}
		else if (roman_number[n] == 'd' or roman_number[n] == 'D') {
			array_of_numbers[n] = d;
		}
		else if (roman_number[n] == 'm' or roman_number[n] == 'M') {
			array_of_numbers[n] = m;
		}
		else {
			cout << "ERROR: simbol " << roman_number[n] << " are not roman number." << endl;
		}
	}
	
	decimal_number = array_of_numbers[length - 1];
	cout << decimal_number << " ";
	for (int m = length - 1; m >= 0; m--) {
		if (array_of_numbers[m] > array_of_numbers[m - 1]) {
			decimal_number -= array_of_numbers[m - 1];
		}
		else {
			decimal_number += array_of_numbers[m - 1];
		}
	}
}

void RomanDecimal::convert_to_roman() {
	if (decimal_number >= 4000 or decimal_number <= 0) {
		roman_number = "NO_NUMBER";
		return;
	}
	int temp_number = decimal_number;
	roman_number = "";
	while (temp_number) {
		if (temp_number >= 1000) {
			roman_number += "M";
			temp_number -= 1000;
		}
		else if (temp_number >= 900) {
			roman_number += "CM";
			temp_number -= 900;
		}
		else if (temp_number >= 500) {
			roman_number += "D";
			temp_number -= 500;
		}
		else if (temp_number >= 100) {
			roman_number += "C";
			temp_number -= 100;
		}
		else if (temp_number >= 90) {
			roman_number += "XC";
			temp_number -= 90;
		}
		else if (temp_number >= 50) {
			roman_number += "L";
			temp_number -= 50;
		}
		else if (temp_number >= 10) {
			roman_number += "X";
			temp_number -= 10;
		}
		else if (temp_number >= 9) {
			roman_number += "IX";
			temp_number -= 9;
		}
		else if (temp_number >= 5) {
			roman_number += "V";
			temp_number -= 5;
		}
		else if (temp_number >= 1) {
			roman_number += "I";
			temp_number -= 1;
		}
	}
}

string RomanDecimal::get_roman() {
	return roman_number;
}

int RomanDecimal::get_decimal() {
	return decimal_number;
}

int main() {
	RomanDecimal number;
	number.add_roman("MDCCCCX");  //number 1910
	cout << "Roman number " << number.get_roman() << " are " << number.get_decimal() << " in decimal." << endl;
	number.add_roman("MCMX");  //number 1910
	cout << "Roman number " << number.get_roman() << " are " << number.get_decimal() << " in decimal." << endl;
	number.add_decimal(1910);
	cout << "Roman number " << number.get_roman() << " are " << number.get_decimal() << " in decimal." << endl;
	number.add_decimal(1858);
	cout << "Roman number " << number.get_roman() << " are " << number.get_decimal() << " in decimal." << endl;
	return 0;
}
Stewbond (2827)
Is that your final solution or do you still have questions?
Shinigami (309)
this is j123t topic not my :D
And this is my solution.
Last edited on
Stewbond (2827)
Sweet, glad you got it. :)
j123t (10)
Wow thanks. Although, my user input is an int.... not a string. so i think i did it wrong? :/
Last edited on
j123t (10)
:/
mik2718 (347)
The Romans used slaves from Greece, Babylonia etc to do their math and then translate the results back to Roman at the end.

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