# Convert Decimal Number to Roman Numeral in C and C++

Here you will get program to convert decimal number to roman numeral in C and C++.

How it Works?

• Divide the given number in the order 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 to find largest base value.
• Display the corresponding roman symbol of largest base value obtained by above method in output.
• Subtract the given number with largest base value to get new number.
• Repeat above process with the new number until it becomes 0.

Example:

Decimal Number: 250

• Divide it in order 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 to find largest base value. Here 250 is divided by 100. The corresponding roman symbol for 100 is C.
• Subtract 250 with 100 (largest base value in previous step) to get new number i.e. 150.
• Again divide 150 in the order mentioned earlier. It is divided by 100, so corresponding roman symbol is C.
• Subtract 150 with 100 to get new number i.e. 50.
• Divide 50 again in the order mentioned earlier. 50 is divided by 50, so corresponding roman symbol is L.
• Subtract 50 with 50. The new number obtained is 0 so we stop here.
• The final roman numeral is CCL.

Below program implements above algorithm.

## Program to Convert Decimal Number to Roman Numeral in C

```#include<stdio.h>

void decimal2roman(int num){
int decimal[] = {1000,900,500,400,100,90,50,40,10,9,5,4,1}; //base values
char *symbol[] = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};  //roman symbols
int i = 0;

while(num){ //repeat process until num is not 0
while(num/decimal[i]){  //first base value that divides num is largest base value
printf("%s",symbol[i]);    //print roman symbol equivalent to largest base value
num -= decimal[i];  //subtract largest base value from num
}
i++;    //move to next base value to divide num
}
}

int main()
{
printf("250 -> ");
decimal2roman(250);

printf("\n1550 -> ");
decimal2roman(1550);

printf("\n670 -> ");
decimal2roman(670);

return 0;
}```

Output

250 -> CCL
1550 -> MDL
670 -> DCLXX

## Program to Convert Decimal Number to Roman Numeral in C++

```#include<iostream>

using namespace std;

void decimal2roman(int num){
int decimal[] = {1000,900,500,400,100,90,50,40,10,9,5,4,1}; //base values
char *symbol[] = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};  //roman symbols
int i = 0;

while(num){ //repeat process until num is not 0
while(num/decimal[i]){  //first base value that divides num is largest base value
cout<<symbol[i];    //print roman symbol equivalent to largest base value
num -= decimal[i];  //subtract largest base value from num
}
i++;    //move to next base value to divide num
}
}

int main()
{
cout<<"250 -> ";
decimal2roman(250);

cout<<"\n1550 -> ";
decimal2roman(1550);

cout<<"\n670 -> ";
decimal2roman(670);

return 0;
}```

Comment below if you any queries related to above program.

### 5 thoughts on “Convert Decimal Number to Roman Numeral in C and C++”

1. The decimal to Roman code doesn’t work properly. It works only for additive cases (i.e. where the Roman symbols all add to each other, like XVI = 36), not for subtractive cases (where the digit on the left gets subtracted), e.g. XIV = 34.

2. Just built something similar except mine did calculations as well. The issue with yours is the lack of error checking for cases such as the 2’s case you can’t have DD for example that would be M, the 3’s can’t have VVV cause XV is 15, then the 4’s case where you can never have more than three in a row. Then you have the -1 a +1 cases… a lot of inputs blow your project up.