function chonthang(thang){
	document.frmcalendar.method = "POST";
	document.frmcalendar.action = "calendar.php?m=" + thang;
	document.frmcalendar.submit();
}

function showPrevMonth() {
	document.getElementById('mon').value = "" + document.getElementById('month').value;
	document.getElementById('yr').value = "" + document.getElementById('year').value;
	if (document.getElementById('mon').value == "") {
		getMonthYear();
	}
	m = eval(document.getElementById('mon').value + "-" + 1);
	if (m < 10) {
		m = "0" + m;
	}
	y = document.getElementById('yr').value;
	if (m < 1) {
		m = 12;
		y = eval(y + "-" + 1);
	}
	window.location.href = "calendar.php?month=" + m + "&year=" + y;
}

function showNextMonth() {
	document.getElementById('mon').value = "" + document.getElementById('month').value;
	document.getElementById('yr').value = "" + document.getElementById('year').value;
	if (document.getElementById('mon').value == "") {
		getMonthYear();
	}
	m = eval(document.getElementById('mon').value + "+" + 1);
	if (m < 10) {
		m = "0" + m;
	}
	y = document.getElementById('yr').value;
	if (m > 12) {
		m = 1;
		y = eval(y + "+" + 1);
	}
	window.location.href = "calendar.php?month=" + m + "&year=" + y;
}

function getMonthYear() {
	cdate = new Date();
	mvalue = cdate.getMonth();
	yvalue = cdate.getYear();
	document.getElementById('mon').value = mvalue;
	document.getElementById('yr').value = yvalue;
}