LL(2)

LL2

#include <iostream>
using namespace std;

/*
Grammar:
	E -> \0 | F;
	F -> d\0 | d+F;
 */

char look_first;
char look_second;

char s[100];

int cur = -1;
void init() {
	cur = -1;
};

char next() {
	cur++;
	return s[cur];
}

bool f_rule();
bool e_rule() {
	look_first = next();
	if (look_first == '\0') {
		return true;
	}
	/* back one step */
	cur--;
	return f_rule();
}

bool f_rule() {
	/* LL(2) */
	look_first = next();
	look_second = next();

	if (look_first == 'd') {
		if (look_second == '\0') {
			return true;
		}
		else if (look_second == '+') {
			return f_rule();
		}
		else {
			return false;
		}
	}
	return false;
}

int main()
{
	strcpy(s, "");
	init();
	cout << s << ":" << e_rule() << endl;

	strcpy(s, "d");
	init();
	cout << s << ":" << e_rule() << endl;

	strcpy(s, "+d");
	init();
	cout << s << ":" << e_rule() << endl;

	strcpy(s, "d+");
	init();
	cout << s << ":" << e_rule() << endl;

	strcpy(s, "d+d");
	init();
	cout << s << ":" << e_rule() << endl;

	strcpy(s, "d+d+d+d");
	init();
	cout << s << ":" << e_rule() << endl;

	return 0;
}