function daysInMonth(month,year) {

	return 32 - new Date(year,month,32).getDate();

}

function addOption(selectbox,text,value,isSelected) {

	var optn = document.createElement("option");
	optn.text = text;
	optn.value = value;
	selectbox.options.add(optn);
	optn.selected = isSelected;	

}

function updateDays(name) {

	var currentDay = document.getElementById(name + "Day").value;

	var month = document.getElementById(name + "Month").value;
	var year = document.getElementById(name + "Year").value;

	var isSelected = false;

	if (month !== "" && year !== "") {

		var newDays = daysInMonth((month - 1),year);

		if (document.getElementById(name + "Day").childNodes.length !== newDays) {

			document.getElementById(name + "Day").innerHTML = "";

			for (i = 0;i < newDays;i ++) {
				isSelected = false;
				if (currentDay == (i + 1)) {
					isSelected = true;
				}
				addOption(document.getElementById(name + "Day"),(i + 1),(i + 1),isSelected);
			}

		}

	}

}