得到两个日期得间隔数，VB中的DateDiff ，我自己写了一个C#的

public enum DateInterval
   {
        Second, Minute, Hour, Day, Week, Month, Quarter, Year
    }
    public  long DateDiff(DateInterval Interval, System.DateTime StartDate, System.DateTime EndDate)
    ...{
        long lngDateDiffValue = 0;
        System.TimeSpan TS = new System.TimeSpan(EndDate.Ticks - StartDate.Ticks);
        switch (Interval)
        ...{
            case DateInterval.Second:
                lngDateDiffValue = (long)TS.TotalSeconds;
                break;
            case DateInterval.Minute:
                lngDateDiffValue = (long)TS.TotalMinutes;
                break;
            case DateInterval.Hour:
                lngDateDiffValue = (long)TS.TotalHours;
                break;
            case DateInterval.Day:
                lngDateDiffValue = (long)TS.Days;
                break;
            case DateInterval.Week:
                lngDateDiffValue = (long)(TS.Days / 7);
                break;
            case DateInterval.Month:
                lngDateDiffValue = (long)(TS.Days / 30);
                break;
            case DateInterval.Quarter:
                lngDateDiffValue = (long)((TS.Days / 30) / 3);
                break;
            case DateInterval.Year:
                lngDateDiffValue = (long)(TS.Days / 365);
                break;
        }
        return (lngDateDiffValue);
    }