Develop Reference

how to get the get first Sunday of the month using date format?

Hi I need to check a condition for the first Sunday of the month for a date formatted as YYYYMMDD
var calDate = data.value; // example 20210502 is sunday
if (first Sunday of the month)
{
do this
}
else
{
do that
}
I need to check the above condition for the first Sunday of the month

Split your problem in two:
parse the string to a DateTime object
var date = DateTime.ParseExact(calDate, "yyyyMMdd", null);
Check if the DateTime object refers to the first sunday in a month. For this, it must obviously be a Sunday and the day part must be in the range 1 to 7:
var isFirstSunday = date.DayOfWeek == DayOfWeek.Sunday && date.Day <= 7;

Thsi function can return true or false if the date is first Sunday of the month or not
private static bool IsFirstSunday(DateTime date)
{
int i = 1;
while (i!=7)
{
if (date.Day==i && date.DayOfWeek == DayOfWeek.Sunday)
{
return true;
}
i++;
}
return false;
}
And use the result in your if condition
//First sunday
var date = DateTime.Parse("2021-05-02 11:27 AM");
var result = IsFirstSunday(date);
//Second sunday
date = DateTime.Parse("2021-05-09 11:27 AM");
result = IsFirstSunday(date);
//Non sunday
date = DateTime.Parse("2021-05-04 11:27 AM");
result = IsFirstSunday(date);

public static DateTime GetFirstSundayOfMonth(DateTime givenDate)
{
DateTime firstDayNextMonth = givenDate.AddDays(-givenDate.Day + 1).AddMonths(1);
int diff = 7 - (int)firstDayNextMonth.DayOfWeek;
return firstDayNextMonth.AddDays(diff);
}

How do I determine if a date lies between current week dates?

In C#,
How we are check certain date with in week dates?
Eg: 6/02/2014
Current Weeks: 02/02/2014 - 08/02/2014
so this dates are with in above week....

Use this for check (last parameter is optional if you want always 1 week from fromDate, you don't need use last parameter):
public static bool DateInside(DateTime checkDate,
DateTime fromDate, DateTime? lastDate = null)
{
DateTime toDate = lastDate != null ? lastDate.Value : fromDate.AddDays(6d);
return checkDate >= fromDate && checkDate <= toDate;
}
To call use:
bool isDateInside = DateInside(new DateTime(2014, 02, 06),
new DateTime(2014, 02, 02)); // return true
And search first :) Answer is also here: How to check whether C# DateTime is within a range
If you want to check if the dates are inside the same week, then you can use this:
public static bool DateInsideOneWeek(DateTime checkDate, DateTime referenceDate)
{
// get first day of week from your actual culture info,
DayOfWeek firstWeekDay = System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;
// or you can set exactly what you want: firstWeekDay = DayOfWeek.Monday;
// calculate first day of week from your reference date
DateTime startDateOfWeek = referenceDate;
while(startDateOfWeek.DayOfWeek != firstWeekDay)
{ startDateOfWeek = startDateOfWeek.AddDays(-1d); }
// fist day of week is find, then find last day of reference week
DateTime endDateOfWeek = startDateOfWeek.AddDays(6d);
// and check if checkDate is inside this period
return checkDate >= startDateOfWeek && checkDate <= endDateOfWeek;
}
Actual week in my culture info start with monday, February 3th 2014 (so for me is week between February 3th and February 9th). If I check any date with reference date (second parameter) as today (2014-Feb-06) I get this results:
For 2014-Feb-02 (Sunday before this week): false
For 2014-Feb-03 (Monday inside this week): true
For 2014-Feb-06 (Today inside this week): true
For 2014-Feb-09 (Sunday inside this week): true
For 2014-Feb-10 (Monday next week): false
You can call this method to check if one date is inside the same week as referentional like this:
DateInsideOneWeek(new DateTime(2014, 02, 02), new DateTime(2014, 02, 06));
You can find current week start and end dates with this code:
DateTime startDateOfWeek = DateTime.Now.Date; // start with actual date
while(startDateOfWeek.DayOfWeek != DayOfWeek.Monday) // set first day of week in your country
{ startDateOfWeek = startDateOfWeek.AddDays(-1d); } // after this while loop you get first day of actual week
DateTime endDateOfWeek = startDateOfWeek.AddDays(6d); // you just find last week day
Is this you wanted?

hmm
public bool isBetween(DateTime input, DateTime date1, DateTime date2)
{
if (input > date1 && input < date2)
return true;
else
return false;
}
?
input= your date
date1 & date2 = start and end of a week

How about:
bool inRange = (date >= lowerDate && date <= upperDate);

Here's another solution :)
public static class DateExtensions
{
private static void Swap<T>(ref T one, ref T two)
{
var temp = one;
one = two;
two = temp;
}
public static bool IsFromSameWeek(this DateTime first, DateTime second, DayOfWeek firstDayOfWeek = DayOfWeek.Monday)
{
// sort dates
if (first > second)
{
Swap(ref first, ref second);
}
var daysDiff = (second - first).TotalDays;
if (daysDiff >= 7)
{
return false;
}
const int TotalDaysInWeek = 7;
var adjustedDayOfWeekFirst = (int)first.DayOfWeek + (first.DayOfWeek < firstDayOfWeek ? TotalDaysInWeek : 0);
var adjustedDayOfWeekSecond = (int)second.DayOfWeek + (second.DayOfWeek < firstDayOfWeek ? TotalDaysInWeek : 0);
return adjustedDayOfWeekSecond >= adjustedDayOfWeekFirst;
}
}
Upd: it appears to have at least twice better performance than #Atiris solution :)

How do I compute a date a specified period in the future?

I have this:
string dataNow = DateTime.Today.tostring();
string dateAfter = dateNow + ( 20 days);
How do I find the date in 20 days?
How do I find the number of days in the month?

Your likely intent is to work with a date as a date type DateTime. In which case, don't call ToString() before you've completed manipulating the date:
string dataNow = DateTime.Today.AddDays(20).ToString();
DateTime.AddDays
After update:
To get the number of days in the current month:
var date = DateTime.Today;
int days = DateTime.DaysInMonth(date.Year, date.Month);
DateTime.DaysInMonth

This should do it:
DateTime dtNow = DateTime.Today;
string dateNow = dtNow.ToString();
string dateAfter = dtNow.AddDays(20).ToString();
int DaysInTheMonth = DateTime.DaysInMonth(dtNow.Year, dtNow.Month);

DateTime today = DateTime.Today;
DateTime later = today.AddDays(20);
string todayAsString = today.ToString("d");
string laterAsString = later.ToString("d");
int daysThisMonth = DateTime.DaysInMonth(today.Year, today.Month);
int daysLaterMonth = DateTime.DaysInMonth(later.Year, later.Month);

Finding Week, using current date ? In C#?

In C# how can i find the week of the current date, i am trying to get the week number of the current date, can you help me, thank you.

See Calendar.GetWeekOfYear
using System;
using System.Globalization;
public class Example
{
public static void Main()
{
DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
DateTime date1 = new DateTime(2011, 1, 1);
Calendar cal = dfi.Calendar;
Console.WriteLine("{0:d}: Week {1} ({2})", date1,
cal.GetWeekOfYear(date1, dfi.CalendarWeekRule,
dfi.FirstDayOfWeek),
cal.ToString().Substring(cal.ToString().LastIndexOf(".") + 1));
}
}
// The example displays the following output:
// 1/1/2011: Week 1 (GregorianCalendar)

If you need current week "global" number, you can use this:
using System;
using System.Globalization;
DateTime date = DateTime.Now;
int res = 0;
// First day of year
res = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstDay, DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek);
// (Default) First four day week from Sunday
res = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Sunday);
// First four day week from StartOfWeek
res = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstFourDayWeek, DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek);
// First full week from Sunday
res = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstFullWeek, DayOfWeek.Sunday);
// First full week from StartOfWeek
res = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date, CalendarWeekRule.FirstFullWeek, DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek);
If you need week number in a month, use smth like such code:
DateTime beginningOfMonth = DateTime.Now;
while (date.Date.AddDays(1).DayOfWeek != CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek)
date = date.AddDays(1);
int result = (int)Math.Truncate((double)date.Subtract(beginningOfMonth).TotalDays / 7f) + 1;

Get the previous month's first and last day dates in c#

I can't think of an easy one or two liner that would get the previous months first day and last day.
I am LINQ-ifying a survey web app, and they squeezed a new requirement in.
The survey must include all of the service requests for the previous month. So if it is April 15th, I need all of Marches request ids.
var RequestIds = (from r in rdc.request
where r.dteCreated >= LastMonthsFirstDate &&
r.dteCreated <= LastMonthsLastDate
select r.intRequestId);
I just can't think of the dates easily without a switch. Unless I'm blind and overlooking an internal method of doing it.

var today = DateTime.Today;
var month = new DateTime(today.Year, today.Month, 1);
var first = month.AddMonths(-1);
var last = month.AddDays(-1);
In-line them if you really need one or two lines.

The way I've done this in the past is first get the first day of this month
dFirstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
Then subtract a day to get end of last month
dLastDayOfLastMonth = dFirstDayOfThisMonth.AddDays (-1);
Then subtract a month to get first day of previous month
dFirstDayOfLastMonth = dFirstDayOfThisMonth.AddMonths(-1);

using Fluent DateTime https://github.com/FluentDateTime/FluentDateTime
var lastMonth = 1.Months().Ago().Date;
var firstDayOfMonth = lastMonth.FirstDayOfMonth();
var lastDayOfMonth = lastMonth.LastDayOfMonth();

DateTime LastMonthLastDate = DateTime.Today.AddDays(0 - DateTime.Today.Day);
DateTime LastMonthFirstDate = LastMonthLastDate.AddDays(1 - LastMonthLastDate.Day);

I use this simple one-liner:
public static DateTime GetLastDayOfPreviousMonth(this DateTime date)
{
return date.AddDays(-date.Day);
}
Be aware, that it retains the time.

An approach using extension methods:
class Program
{
static void Main(string[] args)
{
DateTime t = DateTime.Now;
DateTime p = t.PreviousMonthFirstDay();
Console.WriteLine( p.ToShortDateString() );
p = t.PreviousMonthLastDay();
Console.WriteLine( p.ToShortDateString() );
Console.ReadKey();
}
}
public static class Helpers
{
public static DateTime PreviousMonthFirstDay( this DateTime currentDate )
{
DateTime d = currentDate.PreviousMonthLastDay();
return new DateTime( d.Year, d.Month, 1 );
}
public static DateTime PreviousMonthLastDay( this DateTime currentDate )
{
return new DateTime( currentDate.Year, currentDate.Month, 1 ).AddDays( -1 );
}
}
See this link
http://www.codeplex.com/fluentdatetime
for some inspired DateTime extensions.

The canonical use case in e-commerce is credit card expiration dates, MM/yy. Subtract one second instead of one day. Otherwise the card will appear expired for the entire last day of the expiration month.
DateTime expiration = DateTime.Parse("07/2013");
DateTime endOfTheMonthExpiration = new DateTime(
expiration.Year, expiration.Month, 1).AddMonths(1).AddSeconds(-1);

If there's any chance that your datetimes aren't strict calendar dates, you should consider using enddate exclusion comparisons...
This will prevent you from missing any requests created during the date of Jan 31.
DateTime now = DateTime.Now;
DateTime thisMonth = new DateTime(now.Year, now.Month, 1);
DateTime lastMonth = thisMonth.AddMonths(-1);
var RequestIds = rdc.request
.Where(r => lastMonth <= r.dteCreated)
.Where(r => r.dteCreated < thisMonth)
.Select(r => r.intRequestId);

DateTime now = DateTime.Now;
int prevMonth = now.AddMonths(-1).Month;
int year = now.AddMonths(-1).Year;
int daysInPrevMonth = DateTime.DaysInMonth(year, prevMonth);
DateTime firstDayPrevMonth = new DateTime(year, prevMonth, 1);
DateTime lastDayPrevMonth = new DateTime(year, prevMonth, daysInPrevMonth);
Console.WriteLine("{0} {1}", firstDayPrevMonth.ToShortDateString(),
lastDayPrevMonth.ToShortDateString());

This is a take on Mike W's answer:
internal static DateTime GetPreviousMonth(bool returnLastDayOfMonth)
{
DateTime firstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
DateTime lastDayOfLastMonth = firstDayOfThisMonth.AddDays (-1);
if (returnLastDayOfMonth) return lastDayOfLastMonth;
return firstDayOfThisMonth.AddMonths(-1);
}
You can call it like so:
dateTimePickerFrom.Value = GetPreviousMonth(false);
dateTimePickerTo.Value = GetPreviousMonth(true);

var lastMonth = DateTime.Today.AddMonths(-1);
dRet1 = new DateTime(lastMonth.Year, lastMonth.Month, 1);
dRet2 = new DateTime(lastMonth.Year, lastMonth.Month, DateTime.DaysInMonth(lastMonth.Year, lastMonth.Month));