Number to Roman Numerals

Roman numbers are non-positional numbers. Some numerals are placed together to form a number in roman numbers. For an example the number 75 can be expressed as 75 = 50 + 10 + 10 + 5, so the roman numerals are LXXV.

In this problem one number is provided in a decimal format, our task is to convert it into the Roman numeral strings.

There are different symbols and their value, like this.

Using this table, we can easily find the roman numerals of a given number.

Input and Output

Input:
Decimal number: 3569
Output:
The Roman equivalent of 3569 is: MMMDLXIX

Algorithm

decToRoman(nuList, num)

Input: The numeral list with its value, number to convert into roman.

Output: The Roman numerals for the given number.

Begin
   if num ≠ 0, then
      max := get maximum numeral value, not greater than number
      display the nuList[max].symbol
      num := num – nuList[max].value
      decToRoman(nuList, num)
End

Example

#include<iostream>
using namespace std;

struct numeral {
   string sym;
   int val;
};

int maxNume(numeral nu[], int num) {
   int index;
   for(int i = 0; i<15; i++)   //15 numerals in array
      if(nu[i].val<= num)
         index = i;
   //gretest value numeral index, not greater than number
   return index;
}

void decToRoman(numeral nu[], int num) {
   int max;
   if(num != 0) {
      max = maxNume(nu, num);
      cout << nu[max].sym;
      num -= nu[max].val;   //decrease number
      decToRoman(nu, num);   //recursively print numerals
   }
}

int main() {
   int number;
   numeral nume[15] = {{"I",1},{"IV",4},{"V",5},{"IX",9},
      {"X",10},{"XL",40},{"L",50},{"XC",90},
      {"C",100},{"CD",400},{"D",500},{"CM",900},
      {"M",1000},{"MMMM",4000},{"V'",5000}
   };
   cout << "Enter a decimal number: "; cin >> number;

   if(number >0 && number <= 5000) {   //checking input number
      cout<<"The Roman equivalent of " << number<<" is: ";
         decToRoman(nume, number);
   }else {
      cout << "Invalid Input";
   }
}

Output

Enter a decimal number: 3569
The Roman equivalent of 3569 is: MMMDLXIX