# C Program to Convert Roman Number to Decimal Number

Let’s understand how to Convert Roman Num to Decimal Num in C Programming Language.

## C Program to Convert Roman Number to Decimal Number

```#include <stdio.h>

/*Learn C Programming at CodeAtGlance.com*/

#include<string.h>
int digit(char);
int main(){
char num1[1000];
int i=0;
long int num =0;
printf("Please enter any roman num (Valid digits are I, V, X, L, C, D, M):  \n");
scanf("%s",num1);
while(num1[i]){
if(digit(num1[i]) < 0){
printf("Invalid roman digit : %c",num1[i]);
return 0;
}
if((strlen(num1) -i) > 2){
if(digit(num1[i]) < digit(num1[i+2])){
printf("Invalid ");
return 0;
}
}

if(digit(num1[i]) >= digit(num1[i+1]))
num = num + digit(num1[i]);
else{
num = num + (digit(num1[i+1]) - digit(num1[i]));
i++;
}
i++;
}
printf("Decimal value =%ld",num);
return 0;
}

int digit(char c){
int value=0;
switch(c){
case 'I': value = 1; break;

case 'V': value = 5; break;

case 'X': value = 10; break;

case 'L': value = 50; break;

case 'C': value = 100; break;

case 'D': value = 500; break;

case 'M': value = 1000; break;

case '\0': value = 0; break;

default: value = -1;

}
return value;
}```