var bannerroot = "/images/banners/";

function nextbanner() {
	if (bannerno() == banners.length - 1) {
		banner.src = bannerroot + banners[0];
	} else {
		banner.src = bannerroot + banners[bannerno() + 1];
	}
}

function prevbanner() {
	if (bannerno() == 0) {
		banner.src = bannerroot + banners[banners.length - 1];
	} else {
		banner.src = bannerroot + banners[bannerno() - 1];
	}
}

function bannerno() {
	for (i = 0; i < banners.length; i++) {
		if (bannerroot + banners[i] == current()) return i;
	}
}

function current() {
    return banner.src.substring(banner.src.indexOf("/", 9), banner.src.length);
}