var monthIndex;
var yearIndex;

function nextMonth(){
	monthIndex = document.forms[0].month.selectedIndex;
	yearIndex  = document.forms[0].year.selectedIndex;
	
	if(monthIndex == document.forms[0].month.length - 1 && yearIndex == 0){
		//do nothing
		
	}else{
		
		monthIndex++;
		
		if(monthIndex > 11){
			monthIndex = 0;
			yearIndex--;
		}
		
		submitTheForm();
	}
	
}

function prevMonth(){
	monthIndex = document.forms[0].month.selectedIndex;
	yearIndex  = document.forms[0].year.selectedIndex;
	
	if(monthIndex == 0 && yearIndex == document.forms[0].year.length - 1){
		//do nothing
		
	}else{
		
		monthIndex--;
		
		if(monthIndex < 0){
			monthIndex = 11;
			yearIndex++;
		}
		
		submitTheForm();
	}
	
}

function submitTheForm(){
	document.forms[0].month.selectedIndex = monthIndex;
	document.forms[0].year.selectedIndex = yearIndex;
	document.forms[0].submit();
}