DateTime Calculation

Here, I have described how to get dates between two dates with an interval of days, such the dates of the last 4 weeks, and how to get the start date and end date with a range.

By this method, you can get dates between two dates with an interval of days or you can use months also. In this method, we have to pass three parameters.

startDate :
endDate
intVal

public static void getDateRange(string startDate, string endDate, int intVal)
{
for (DateTime date = DateTime.Parse(startDate); date <= DateTime.Parse(endDate); date = date.AddDays(intVal))
{
Console.WriteLine(date.ToString("yyyy-MM-dd"));
}
}

In the above method, we will get the dates with an interval of 2 days. Now, call the getDateRange.

public static void Main()
{
getDateRange("2019-01-01", "2019-01-30", 2);
}

Get The Date Range of the Last 4 Weeks

In this method, we have to pass one parameter, i.e., year, and get the last four-week start date and end date.

public static void getLast4WeekRanges(int year)
{
int dd = int.Parse(DateTime.Now.ToString("dd"));
int mm = int.Parse(DateTime.Now.ToString("MM"));
string currentDayinYear = new DateTime(year, mm, dd).ToString("yyyy-MM-dd");
DayOfWeek dDay = DateTime.Now.DayOfWeek;
int days = dDay - DayOfWeek.Monday;
string lastWeekDay;
if (days == 0)
{
lastWeekDay = DateTime.Now.AddDays(-7).ToString("yyyy-MM-dd");
}
else
{
lastWeekDay = DateTime.Now.AddDays(-days).ToString("yyyy-MM-dd");
}
string lastWeekEndDay = DateTime.Parse(lastWeekDay).AddDays(6).ToString("yyyy-MM-dd");
Console.WriteLine("startdate: {0}, enddate: {1}, currentweek: {2}", lastWeekDay, lastWeekEndDay, true);
for (int i = 0; i < 3; i++)
{
lastWeekDay = DateTime.Parse(lastWeekDay).AddDays(-7).ToString("yyyy-MM-dd");
lastWeekEndDay = DateTime.Parse(lastWeekDay).AddDays(6).ToString("yyyy-MM-dd");
Console.WriteLine("startdate: {0}, enddate: {1}, currentweek: {2}", lastWeekDay, lastWeekEndDay, false);
}
}

Now, call the getLast4WeekRanges.

public static void Main()
{
getLast4WeekRanges(2019);
}

Get start date and end date with a day range

In this method, we will pass a day range like TODAY, LASTWEEK, LASTMONTH, etc and get the start and end date.

public static void getStartEndDate(string dateRange)
{
string startDate, endDate;
string currentDate = DateTime.Now.ToString("yyyy-MM-dd");
switch (dateRange)
{
case "TODAY":
startDate = currentDate;
endDate = currentDate;
break;
case "LASTWEEK":
DayOfWeek desiredDay = DayOfWeek.Monday;
int offsetAmount = (int)desiredDay - (int)DateTime.Now.DayOfWeek;
DateTime lastWeekDesiredDay = DateTime.Now.AddDays(-7 + offsetAmount);
startDate = lastWeekDesiredDay.ToString("yyyy-MM-dd");
endDate = DateTime.Parse(startDate).AddDays(6).ToString("yyyy-MM-dd");
break;
case "LASTMONTH":
DateTime LastMonthLastDate = DateTime.Now.AddDays(0 - DateTime.Now.Day);
DateTime LastMonthFirstDate = LastMonthLastDate.AddDays(1 - LastMonthLastDate.Day);
startDate = LastMonthFirstDate.ToString("yyyy-MM-dd");
endDate = LastMonthLastDate.ToString("yyyy-MM-dd");
break;
case "MONTHLY":
startDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).ToString("yyyy-MM-dd");
endDate = currentDate;
break;
case "LASTTHREEMONTHS":
DateTime LastMonthLastDate1 = DateTime.Now.AddDays(0 - DateTime.Now.Day);
DateTime LastMonthFirstDate1 = LastMonthLastDate1.AddDays(1 - LastMonthLastDate1.Day);
startDate = LastMonthFirstDate1.AddMonths(-2).ToString("yyyy-MM-dd");
endDate = LastMonthLastDate1.ToString("yyyy-MM-dd");
break;
case "YEARLY":
startDate = new DateTime(DateTime.Now.Year, 1, 1).ToString("yyyy-MM-dd");
endDate = currentDate;
break;
default:
startDate = currentDate;
endDate = currentDate;
break;
}
Console.WriteLine("startdate: {0}, enddate: {1}", startDate, endDate);
}

Now, call the getStartEndDate.

public static void Main()
{
getStartEndDate("TODAY");
getStartEndDate("LASTWEEK");
getStartEndDate("LASTMONTH");
getStartEndDate("MONTHLY");
getStartEndDate("LASTTHREEMONTHS");
getStartEndDate("YEARLY");
}