function DaysForSelectedMonth(ddDayId, ddMonthId, ddYearId) {
    var dayCounter = 31;
  
    if (IsObj(ddMonthId))
    { }
    else {
        ddMonthObj = ById(ddMonthId);
    }

    var month = ddMonthObj.value;

    var year = ById(ddYearId).value;
   
    //Leap year?
    if ((year % 4) == 0) {
      
        switch (month) {
            case "2":
                dayCounter = "29";
                break;
            case "4":
                dayCounter = "30";
                break;
            case "6":
                dayCounter = "30";
                break;
            case "9":
                dayCounter = "30";
                break;
            case "11":
                dayCounter = "30";
                break;
        }
    }
    else {
           switch (month) {
            case "2":
                dayCounter = "28";
                break;
            case "4":
                dayCounter = "30";
                break;
            case "6":
                dayCounter = "30";
                break;
            case "9":
                dayCounter = "30";
                break;
            case "11":
                dayCounter = "30";
                break;
        }

    }
    var dropDownDay = ById(ddDayId);
    
    if (dropDownDay.length > dayCounter) {        
        for (var i = dropDownDay.length; i > dayCounter; i--) {           
            dropDownDay.remove(i - 1);
        }
    }
    else if (dropDownDay.length < dayCounter) {      
        for (var i = dropDownDay.length; i < dayCounter; i++) {
            var option = document.createElement('option');
            option.value = i + 1;
            option.text = i + 1;
            try {
                dropDownDay.add(option, null);
            }
            catch (err) {
                dropDownDay.add(option);
            }
        }
    }
}