#include "遞歸下降法整數運算.h"

char TOKEN;

void get_token () {
	TOKEN = getchar ();
}
void match (char c) {
	if (TOKEN == c) get_token ();
}
int command () {
	int result = expression ();

	return result;
}
int expression () {
	int result = term ();

	while (TOKEN == '+' || TOKEN == '-') {
		char tmp = TOKEN; 
		get_token ();
		tmp == '+' ? 
			result += term () : result -= term ();
	}

	return result;
}
int term () {
	int result = factor ();

	while (TOKEN == '*' || TOKEN == '/') {
		char tmp = TOKEN;
		get_token ();
		tmp == '*' ? 
			result *= factor () : result /= factor ();
	}

	return result;
}
int factor () {
	int result;

	if (TOKEN == '(') {
		get_token ();
		result = expression ();
		match (')');
	} else
		result = number ();

	return result;
}
int number () {
	int result = digit ();

	get_token ();
	while (TOKEN <= 57 && TOKEN >= 48) {
		result = 10 * result + digit ();
		get_token ();
	}
	
	return result;
}
int digit () {
	int result = TOKEN - '0';
	return result;
}
void parse () {
	get_token ();
	int result = command ();

	printf ("The result of this expression is: %d\n", result);
}