C program to convert Roman number to decimal number

C code for roman numbers to English numbers

#include<stdio.h>

#include<string.h>

int digitValue(char);

int main(){

    char roman_Number[1000];

    int i=0;

    long int number =0;

   

    printf("Enter any roman number (Valid digits are I, V, X, L, C, D, M):  \n");

    scanf("%s",roman_Number);

   

    while(roman_Number[i]){

        

         if(digitValue(roman_Number[i]) < 0){

             printf("Invalid roman digit : %c",roman_Number[i]);

             return 0;

         }

            

         if((strlen(roman_Number) -i) > 2){

             if(digitValue(roman_Number[i]) < digitValue(roman_Number[i+2])){

                 printf("Invalid roman number");

                 return 0;

             }

         }

         if(digitValue(roman_Number[i]) >= digitValue(roman_Number[i+1]))

             number = number + digitValue(roman_Number[i]);

         else{

             number = number + (digitValue(roman_Number[i+1]) - digitValue(roman_Number[i]));

             i++;

         }

         i++;

    }

        

    printf("Its decimal value is : %ld",number);

   

    return 0;

}

int digitValue(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;

}

Sample output:

Enter any roman number (Valid digits are I, V, X, L, C, D, M):

XVII

Its decimal value is: 17