Roman_to_Decimal.c

/*Name :  Atul Kumar
Github username : atul1510
Repositary name : Algorithms
*/
/* Problem Statement : Given a Roman numeral, the task is to convert it into its decimal equivalent.
EXAMPLES : 
1)
Input:  "XXI"
Output: 21
2)
Input:  "MCMXCIV"
Output: 1994 */
#include <stdio.h>
#include <string.h>
// Function to return the decimal equivalent of a Roman numeral
int value(char c)
{
    if (c == 'I')
        return 1;
    if (c == 'V')
        return 5;
    if (c == 'X')
        return 10;
    if (c == 'L')
        return 50;
    if (c == 'C')
        return 100;
    if (c == 'D')
        return 500;
    if (c == 'M')
        return 1000;
    // If the character is not a valid Roman numeral
    return -1;
}
// Function to convert Roman numeral to decimal
int romanToDecimal(char str[])
{
    int result = 0;
    int prev = 0;
    int len = strlen(str);
    // Iterating over each character in the input string in reverse order
    for (int i = len - 1; i >= 0; i--)
    {
        int curr = value(str[i]);
        if (curr >= prev)
        {
            // If the value of the current symbol is greater than or equal to the value of the previous symbol, add it to the result
            result += curr;
        }
        else
        {
            // If the value of the current symbol is less than the value of the previous symbol, subtract it from the result
            result -= curr;
        }
        prev = curr;
    }
    return result;
}
int main()
{
    char str[100];
    printf("Enter a Roman numeral: ");
    fgets(str, sizeof(str), stdin);
    printf("Decimal equivalent: %d\n", romanToDecimal(str));
    return 0;
}