Convert Roman Numerals to Decimal in C++

In this tutorial, we will be discussing a program to converting roman numerals to decimal lying between 1 to 3999.

For this we will be provided with a random roman numeral. Our task is to convert the given roman numeral into its decimal equivalent.

Example

 Live Demo

#include<bits/stdc++.h>
using namespace std;
//calculating the decimal value
int value(char r){
   if (r == 'I')
   return 1;
   if (r == 'V')
   return 5;
   if (r == 'X')
   return 10;
   if (r == 'L')
   return 50;
   if (r == 'C')
   return 100;
   if (r == 'D')
   return 500;
   if (r == 'M')
   return 1000;
   return -1;
}
//calculating decimal equivalent of given numeral
int convert_decimal(string &str){
   int res = 0;
   for (int i=0; i<str.length(); i++){
      //getting value of digit
      int s1 = value(str[i]);
      if (i+1 < str.length()){
         int s2 = value(str[i+1]);
         if (s1 >= s2){
            res = res + s1;
         }
         else{
            res = res + s2 - s1;
            i++;
         }
      }
      else{
         res = res + s1;
      }
   }
   return res;
}
int main(){
   string str ="MCMIV";
   cout << "Integer form:"
   << convert_decimal(str) << endl;
   return 0;
}

Output

Integer form:1904