roman.c

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

#define bool int
#define true 1
#define false 0

int get_value(char roman_number) {
	switch(roman_number) {
		case 'I':
		case 'i':
			return 1;
		case 'X':
		case 'x':
			return 10;
		case 'C':
		case 'c':
			return 100;
		case 'M':
		case 'm':
			return 1000;
		case 'V':
		case 'v':
			return 5;
		case 'L':
		case 'l':
			return 50;
		case 'D':
		case 'd':
			return 500;
		default:
			printf("1: Invalid number");
			exit(2);
	}
}

bool is_aux_num(int number) {
	switch(number){
		case 5:
		case 50:
		case 500:
			return true;
		default:
			return false;
	}
}

int main(int argc, char *argv[]) {
	char *roman_value;
	int i;
	int current_value;
	int next_value;
	int final_value = 0;
	bool last_op_sub = false; // false == add, true == sub

	char last_char;
	int last_char_count;
	int V_count = 0;
	int L_count = 0;
	int D_count = 0;

	int last_additive_num = -1;
	int last_sub_num = -1;
	int last_sub_pos = -1;

	if(argc != 2) {
		printf("Invalid usage\n");
		printf("Usage: roman roman_numeral\n");
		exit(1);
	}

	roman_value = argv[1];

//	printf("%s\n", roman_value);

	for(i = 0; i < strlen(roman_value); i++) {

		if(V_count > 1 || L_count > 1 || D_count > 1) {
			printf("2: Invalid number");
			exit(2);
		}

		if(last_char == roman_value[i]) {
			last_char_count++;
			if(last_char_count == 4) {
				printf("3: Invalid number");
				exit(2);
			} 
		} else {
			last_char = roman_value[i];
			switch(last_char) {
				case 'V': case 'v':
					V_count++;
					break;
				case 'L': case 'l':
					L_count++;
					break;
				case 'D': case 'd':
					D_count++;
					break;
			}
			last_char_count = 1;
		}

		current_value = get_value(roman_value[i]);
		if(last_additive_num != -1 && current_value > last_additive_num) {
			printf("4: Invalid number");
			exit(2);
		}
		if(last_sub_num != -1 && current_value >= last_sub_num && last_sub_pos != i-1) {
			printf("7: Invalid number");
			exit(2);
		}
		if(i < strlen(roman_value) - 1) {
			next_value = get_value(roman_value[i+1]);
			if(current_value < next_value) {
				if(last_op_sub == true || is_aux_num(current_value)) {
					printf("5: Invalid number");
					exit(2);
				}
				if(current_value < next_value / 10) {
					printf("6: Invalid number");
					exit(2);
				}
				final_value -= current_value;
				last_sub_num = current_value;
				last_sub_pos = i;
				last_op_sub = true;
			} else {
				final_value += current_value;
				last_additive_num = current_value;
				last_op_sub = false;
			}
		} else {
			final_value += current_value;
			last_additive_num = current_value;
			last_op_sub = false;
		}
	}

	printf("%d", final_value);
	return 0;
}