Decimal to Roman converter

/*  Overly complex (but correct) program written by me.
    Compare http://pastebin.com/HnceuR19
*/

#include <stdio.h>
#include <ctype.h>

int single_char(char roman)
{
    roman = tolower(roman);
    switch(roman)
    {
        case 'i': return 1;
        case 'v': return 5;
        case 'x': return 10;
        case 'l': return 50;
        case 'c': return 100;
        case 'd': return 500;
        case 'm': return 1000;
        default:  return 0;
    }
}

int roman_to_decimal(char *roman)
{
    int i, prev_val = 0, cur_val, committed_all = 0, result = 0;
    char cur;

    for(i = 0; roman[i] != '\0'; i++)
    {
        cur_val = single_char(roman[i]);
        if (cur_val > prev_val && i != 0)
        {
            result += cur_val - prev_val;
            committed_all = 1;
        }
        else
        {
            if (!committed_all)
                result += prev_val;
            committed_all = 0; // current value uncommitted
        }

        prev_val = cur_val;
    }

    if (!committed_all)
        result += cur_val;

    return result;
}

int main()
{
    char roman[20];
    int result;
    printf("Enter Roman number: ");
    scanf("%s", roman);
    result = roman_to_decimal(roman);
    printf("Decimal equivalent: %d\n", result);
    printf("\n");
}