Integer to Roman in C

Given a decimal number n, we have to convert this into Roman numeral. The value n lies in the range 1 to 4000. These are some Roman Numerals.

So if the number n = 859, its Roman Numeral will be DCCCLIX

To solve this, we will follow these steps

• Define an array to store numeral and corresponding values for the given list. That is called nume array
• we are using a recursive approach, the function decToRom() is used. this is taking nume array and the number num.
• The decToRom() will be like
• if num is not 0, then
  • max := find maximum value from nume array that is not larger than num
  • append the value for that max into the result string
  • num := num – max value
  • decToRom(nume, num)

Example

Let us see the following implementation to get a better understanding −

#include<stdio.h> typedef struct{    char *sym;    int val; }numeral; int maxNume(numeral *nu, int num){    int i, index;    for(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);       printf("%s", nu[max].sym);       num -= nu[max].val;//decrease number       decToRoman(nu, num);//recursively print numerals    } } 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}};    printf("Enter a decimal number: ");    scanf("%d", &number);    if(number >0 && number <= 5000){//checking input number       printf("The Roman equivalent of %d is ", number);       decToRoman(nume, number);    }    else{       printf("Invalid Input");    }    printf("
"); }

Input

570 3574

Output

DLXX MMMDLXXIV