/***********************************************
* Section : 15
* Machine No. : N
* Roll No. : 19CS100XY
* Name : Aritra Hazra
* Assignment No : 6B
* Description : Roman String to Decimal Numbers
***********************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_SIZE 1000

/* function to return the decimal equivalent value of a roman number character */
int getRomanValue(char r) 
{
    int val;
    switch(r) {
        case 'I': val =    1; break;
        case 'V': val =    5; break;
        case 'X': val =   10; break;
        case 'L': val =   50; break;
        case 'C': val =  100; break;
        case 'D': val =  500; break;
        case 'M': val = 1000; break;
        default : val =   -1; break; // illegal case
    }
    return val;
}

/* function to convert the roman number into decimal equivalent, and also print the conversion breakup values */
unsigned long int romanToDecimal(char *romanNum)
{
    unsigned long int decimalNum = 0;
    unsigned int i = 0, romanLen = strlen(romanNum), romanVal1, romanVal2;
    
    for(i=0; i<romanLen; i++) {
        romanVal1 = getRomanValue(romanNum[i]);
        if(romanVal1 == -1) break; // illegal case
        if((i+1) < romanLen) {
            romanVal2 = getRomanValue(romanNum[i+1]);
            if(romanVal2 == -1) break; // illegal case
            if(romanVal1 >= romanVal2) { /* incremental decimal values obtained from consecutive roman characters addition (e.g. XI) */
                decimalNum += romanVal1;
                if(i>0) printf(" +");
                printf(" %c [%u]", romanNum[i], romanVal1);
            }
            else { /* decremental decimal values obtained from consecutive roman characters subtraction (e.g. IX) */
                decimalNum += romanVal2 - romanVal1;
                if(i>0) printf(" +");
                printf(" %c%c [%u]", romanNum[i], romanNum[i+1], romanVal2-romanVal1);
                i++;
            }
        }
        else { /* end of roman string with one character to convert */
            decimalNum += romanVal1;
            if(i>0) printf(" +");
            printf(" %c [%u]", romanNum[i], romanVal1);
        }
    }
    
    return decimalNum;
}

int main ()
{
    char roman[MAX_SIZE];
    unsigned long int decimal;
    
    printf("Enter Roman String: ");
    scanf("%s", roman);
    
    printf("Decimal Conversion Breakup:");
    decimal = romanToDecimal(roman);
    printf("\nEquivalent Decimal Number : %lu\n", decimal);
    
    return 0;
}