function updateNumDays (aDayControl, aMonth, aYear)
{
  var numDays = getNumDays (aMonth, aYear);

  while (aDayControl.options.length > numDays)
  {
    aDayControl.options.remove (numDays);
  }
  
  while (aDayControl.options.length < numDays)
  {
    var day = aDayControl.options.length + 1;
    var option = document.createElement("OPTION");
    aDayControl.options.add (option);
    option.innerText = day;
    option.value = day;
  }
}


function getNumDays (aMonth, aYear)
{
	if (aMonth == '2')
	{
		if (aYear % 4 == 0)
		{
			return 29;
		}
		else
		{
			return 28;
		}
	}
	else if (aMonth == '1' || aMonth == '3' || aMonth == '5' || aMonth == '7' || aMonth == '8' || aMonth == '10' || aMonth == '12')
	{
		return 31;
	}
	else
	{
		return 30;
	}
}