var icon_dir = 'images/icons/';

function $(id) {
	return document.getElementById(id);
}
function random(max) {
	return Math.floor(Math.random()*max+1);
}
function showRandomIcon(category_name, max_icons) {
	$(category_name).src = icon_dir + category_name + random(max_icons) + '.jpg';
}
function randomizeIcons() {
	categories = [['math',11],['physics',3],['biology',10],['chemistry',9],['space',1],['astronomy',1]];
	for (i=0; i<categories.length; i++) {
		category = categories[i];
		showRandomIcon(category[0], category[1]);
	}
}