Develop Reference

How to select weekends with an interval between them?

How can I select all weekends until the end of the year, with some criteria to be followed?
User input desired Weekend day:
18/12/2021
Software must out:
25/12/2022 (must be ignored)
01/01/2022
08/01/2022 (must be ignored)
15/01/2022
22/01/2022 (must be ignored)
29/01/2022 and so on...
What i have now:
public void GetWeekends() {
var lastWorkedWeekend = dateTimePicker1.Value;
var workedInSunday = checkBox1.Checked;
var list = new List < DateTime > ();
var weekends = GetDaysBetween(lastWorkedWeekend, DateTime.Today.AddDays(365)).Where(d => d.DayOfWeek == DayOfWeek.Saturday);
var selected = true;
for (int i = 0; i < weekends.Count(); i++) {
if (selected == false) {
list.Add(weekends.ElementAt(i));
selected = true;
} else {
selected = false;
}
}
}

I think I'd just scroll the input day forward until it was saturday (or calculate it, but i find the loop more self documenting than casting DayOfWeek to an int and factoring for sunday being 0) then add 14 days repeatedly. This skips over the 25th, etc..
var d = new DateTime(2021, 12, 18);
while(d.DayOfWeek != DayOfWeek.Saturday)
d += TimeSpan.FromDays(1);
while(d.Year == 2021){ //was your 2022 a typo? or maybe make this <= 2022.. I'm not sure what you want there..
d += TimeSpan.FromDays(14);
Console.WriteLine(d);
}
You might prefer DateTime.AddDays()..

Looks to me that you want to get the date of every second weekend from an initial date until the end of the year. In your example, you kinda bleed over to the next year.
public static void Main()
{
var dates = GetDateTimeRange(new DateTime(2021, 12, 18), new DateTime(2023, 1, 1), TimeSpan.FromDays(14));
foreach (var dateTime in dates.Skip(1))
{
Console.WriteLine(dateTime);
}
}
public static IEnumerable<DateTime> GetDateTimeRange(DateTime startingDate, DateTime endDate, TimeSpan interval)
{
var lastDate = startingDate;
while (lastDate < endDate)
{
yield return lastDate;
lastDate = lastDate.Add(interval);
}
}
This returns
01/01/2022 00:00:00
01/15/2022 00:00:00
01/29/2022 00:00:00
02/12/2022 00:00:00
02/26/2022 00:00:00
03/12/2022 00:00:00
03/26/2022 00:00:00
04/09/2022 00:00:00
04/23/2022 00:00:00
05/07/2022 00:00:00
05/21/2022 00:00:00
06/04/2022 00:00:00
06/18/2022 00:00:00
07/02/2022 00:00:00
07/16/2022 00:00:00
07/30/2022 00:00:00
08/13/2022 00:00:00
08/27/2022 00:00:00
09/10/2022 00:00:00
09/24/2022 00:00:00
10/08/2022 00:00:00
10/22/2022 00:00:00
11/05/2022 00:00:00
11/19/2022 00:00:00
12/03/2022 00:00:00
12/17/2022 00:00:00
12/31/2022 00:00:00

One approach is to use a method that creates an enumerable of dates. Once that's done you can use LINQ queries. If creating that enumerable is expensive you could just create one large range encompassing years and re-use it.
Or you might find better performance by just creating the range you need for each query.
public static class DateRanges
{
public static IEnumerable<DateOnly> GetRange(DateOnly start, DateOnly end)
{
for (var date = start; date <= end; date = date.AddDays(1))
{
yield return date;
}
}
}
It's not clear from your code what the criteria is, but this does what you described - all weekends from now to the end of the year.
var today = DateOnly.FromDateTime(DateTime.Today);
var lastDayOfYear = DateOnly.FromDateTime(new DateTime(DateTime.Today.Year, 12, 31));
var dates = DateRanges.GetRange(today, lastDayOfYear);
var weekendsOnly = dates.Where(date =>
date.DayOfWeek == DayOfWeek.Saturday);
Or if you prefer to create one date range and query it repeatedly:
// Big range of dates, 10 years into past and future.
// Create this once and re-use it
var dates = DateRanges.GetRange(
DateOnly.FromDateTime(DateTime.Today.AddYears(-10)),
DateOnly.FromDateTime(DateTime.Today.AddYears(10)));
var today = DateOnly.FromDateTime(DateTime.Today);
var lastDayOfYear = DateOnly.FromDateTime(new DateTime(DateTime.Today.Year, 12, 31));
var weekendsOnly = dates.Where(date =>
date >= today
&& date <= lastDayOfYear
&& date.DayOfWeek == DayOfWeek.Saturday);
In either case if you want every other Saturday you can add
.Where((date, i) => i % 2 == 0);
Or to maintain that readability you could put that in another extension like
public static IEnumerable<T> EveryOther<T>(this IEnumerable<T> source)
{
return source.Where((date, i) => i % 2 == 0);
}
so your query looks like
var everyOtherWeekend = dates
.Where(date =>
date >= today
&& date <= lastDayOfYear
&& date.DayOfWeek == DayOfWeek.Saturday)
.EveryOther();
I wouldn't position this as a better answer than those that iterate over a series of dates. The difference is that instead of having to write a method for any query you can start with a range of dates and then use LINQ to filter it. That makes it a little easier to read and to compose different queries.

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);
}

If birth date is in current week return true

I am doing my lab hw. There is a part that I couldn't handle it: "The company wants to give bonus 200 TL to the employee if the current week is the one in which the employee’s birthday occurs." I am trying to write a method that returns boolean, if the birth date in the current week. Then, I realised that the method I have done is just checking if the current day is equalt to birth date. What I want is if the current payment week if inculdes someone's birthdate. I think I need to use a calendar or something like that. Since the program is temp, each day will be payment day. I mean if the birthday is in the same week with DateTime.Today then return true. And add 200 TL more to the salary.
protected bool isBirthDay()
{
try
{
string today = DateTime.Today.
string birth_date = birthDate.ToString("d");
if (today[0]== birth_date[0] && today[1]== birth_date[1] && today[3]==birth_date[3] && today[4]==birth_date[4])
return true;
return false;
}
catch (Exception e)
{
Console.WriteLine(e);
throw;
}
}

This is more complex than I initially thought. Fortunately the DateTime structure has a method called DayOfYear that could simplify our calculation because we can remove the Year problem and the leap year checks
bool isBirthWeek(DateTime birthDate)
{
DateTime dtStart = DateTime.Today;
// Find the previous monday
while (dtStart.DayOfWeek != DayOfWeek.Monday)
{
dtStart = dtStart.AddDays(-1);
}
DateTime dtEnd = dtStart.AddDays(7);
int dayStart = dtStart.DayOfYear;
int dayEnd = dtEnd.DayOfYear;
int birthDay = birthDate.DayOfYear;
return (birthDay >= dayStart && birthDay < dayEnd);
}
A more generic version could replace the DateTime.Today with a custom date passed from the caller
bool isBirthWeek(DateTime dtStart, DateTime birthDate)
{
// Find the previous monday
while (dtStart.DayOfWeek != DayOfWeek.Monday)
{
dtStart = dtStart.AddDays(-1);
}
DateTime dtEnd = dtStart.AddDays(7);
int dayStart = dtStart.DayOfYear;
int dayEnd = dtEnd.DayOfYear;
int birthDay = birthDate.DayOfYear;
return (birthDay >= dayStart && birthDay < dayEnd);
}
but if you just want to know if the birthdate is inside the range of 6 day before the payment date you could write
bool isBirthWeek(DateTime payDate, DateTime birthDate)
{
DateTime dtStart = payDate.AddDays(-6);
DateTime dtEnd = payDate;
int dayStart = dtStart.DayOfYear;
int dayEnd = dtEnd.DayOfYear;
int birthDay = birthDate.DayOfYear;
return (birthDay >= dayStart && birthDay < dayEnd);
}

I think people are making this too difficult.
/// <summary>
/// Returns True birthdate is in the same week as the compareDate, with Sunday being the start of the week
/// </summary>
/// <param name="compareDate"></param>
/// <param name="birthdate"></param>
/// <returns></returns>
public static bool IsInSameWeek(DateTime compareDate, DateTime birthdate)
{
var startDate = compareDate.AddDays(-(int)compareDate.DayOfWeek); //get the Sunday of the week
if (!DateTime.IsLeapYear(startDate.Year) && birthdate.Month == 2 && birthdate.Day == 29)
birthdate = birthdate.AddDays(-1);
var compareBd = new DateTime(startDate.Year, birthdate.Month, birthdate.Day); //get the birth date of the compare year
var totalDays = (compareBd - startDate).TotalDays; //number of days between the dates.
return (totalDays >= 0 && totalDays <= 6); //Are we within 6 days of each other
}
As the comments point out, we get the start of the week of "compareDate", with Sunday being defined as the start of the week.
We then create a new DateTime with the birth month and day of the year of "compareDate".
Then we make sure the new birthday is equal to the compare date, but no more than 6 days older.

Get all the dates of current week

Say I consider Sunday - Saturday as a week, how do I get all the dates of the current week in c#?
For example, current date is 30th March 2017, the output I need is,
26-March-2017,
27-March-2017,
28-March-2017,
29-March-2017,
30-March-2017,
31-March-2017,
01-April-2017

You can try DateTimeFormat to find out current week's starting date and Linq to generate the string:
DateTime startOfWeek = DateTime.Today.AddDays(
(int) CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek -
(int) DateTime.Today.DayOfWeek);
string result = string.Join("," + Environment.NewLine, Enumerable
.Range(0, 7)
.Select(i => startOfWeek
.AddDays(i)
.ToString("dd-MMMM-yyyy")));
In case of en-US culture you'll get (week starts from Sunday)
26-March-2017, // <- starts from Sunday
27-March-2017,
28-March-2017,
29-March-2017,
30-March-2017,
31-March-2017,
01-April-2017
In case of, say, ru-RU culture you'll get (week starts from Monday)
27-марта-2017, // <- Starts from Monday
28-марта-2017,
29-марта-2017,
30-марта-2017,
31-марта-2017,
01-апреля-2017,
02-апреля-2017

Assuming that Sunday will be the start day of the week, as it is mentioned in the question I suggest following solution.
var today = DateTime.Now.Date; // This can be any date.
Console.WriteLine(today.DayOfWeek);
var day = (int)today.DayOfWeek; //Number of the day in week. (0 - Sunday, 1 - Monday... and so On)
Console.WriteLine(day);
const int totalDaysOfWeek = 7; // Number of days in a week stays constant.
for (var i = -day; i < -day + totalDaysOfWeek; i++)
{
Console.WriteLine(today.AddDays(i).Date);
}

I found this here
DayOfWeek Day = DateTime.Now.DayOfWeek;
int Days = Day - DayOfWeek.Monday; //here you can set your Week Start Day
DateTime WeekStartDate = DateTime.Now.AddDays(-Days);
DateTime WeekEndDate1 = WeekStartDate.AddDays(1);
DateTime WeekEndDate2 = WeekStartDate.AddDays(2);
DateTime WeekEndDate3 = WeekStartDate.AddDays(3);
DateTime WeekEndDate4 = WeekStartDate.AddDays(4);
DateTime WeekEndDate5 = WeekStartDate.AddDays(5);
DateTime WeekEndDate6 = WeekStartDate.AddDays(6);

In my opinion, an extension method is the most useful approach:
public static IEnumerable<DateTime> GetDatesOfWeek(this DateTime date, CultureInfo ci) {
Int32 firstDayOfWeek = (Int32) ci.DateTimeFormat.FirstDayOfWeek;
Int32 dayOfWeek = (Int32) date.DayOfWeek;
DateTime startOfWeek = date.AddDays(firstDayOfWeek - dayOfWeek);
var valuesDaysOfWeek = Enum.GetValues(typeof(DayOfWeek)).Cast<Int32>();
return valuesDaysOfWeek.Select(v => startOfWeek.AddDays(v));
}
Use as follows:
DateTime myDate = DateTime.Today;
IEnumerable<DateTime> result = myDate.GetDatesOfWeek(CultureInfo.CurrentCulture);
foreach ( DateTime d in result ) {
Console.WriteLine(d);
}

get nth weekday of month in C# [duplicate]

This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
How do I determine if a given date is Nth weekday of the month?
How do i get the nth weekday of the month?
For ex.:
2nd Monday of "July 2010" = 07/12/2010.
Looking for a function like:
public DateTime GetNthWeekofMonth(DateTime date, int nthWeek, DayOfWeek dayofWeek)
{
//return the date of nth week of month
}
from the above, the parameters of the function will be ("Any Date in July 2010", 2, Monday).

Use the following extension method:
public static class DateTimeExtensions
{
///<summary>Gets the first week day following a date.</summary>
///<param name="date">The date.</param>
///<param name="dayOfWeek">The day of week to return.</param>
///<returns>The first dayOfWeek day following date, or date if it is on dayOfWeek.</returns>
public static DateTime Next(this DateTime date, DayOfWeek dayOfWeek) {
return date.AddDays((dayOfWeek < date.DayOfWeek ? 7 : 0) + dayOfWeek - date.DayOfWeek);
}
}
You can then write
new DateTime(2010, 07, 01).Next(DayOfWeek.Monday).AddDays((2 - 1) * 7);
Or, as a function:
public DateTime GetNthWeekofMonth(DateTime date, int nthWeek, DayOfWeek dayOfWeek) {
return date.Next(dayOfWeek).AddDays((nthWeek - 1) * 7);
}
(I need to subtract one because date.Next(dayOfWeek) is already the first occurrence of that day)

One possible algorithm:
Start from the 1st of the month.
Move forward one day at a time until
you get the Day of Week you're
looking for.
Add (7 * N) to the date you're on to
get the date you want.

Duplicate can be found here: How do I determine if a given date is the Nth weekday of the month?
int d = date.Day;
return date.DayOfWeek == dow && (d-1)/7 == (n-1);

IEnumerable<DateTime> WeekdaysFrom( DateTime start )
{
DateTime weekday = start.Add( TimeSpan.FromDays(1) );
while( weekday < DateTime.MaxValue.Subtract( TimeSpan.FromDays(1) ) )
{
while( weekday.DayOfWeek == DayOfWeek.Saturday || weekday.DayOfWeek == DayOfWeek.Sunday )
{
weekday.Add( TimeSpan.FromDays(1) );
}
yield return weekday;
}
}
DateTime NthWeekday( DateTime month, int n )
{
return WeekdaysFrom( new DateTime( month.year, month.month, 1 ) ).Skip(n-1).First();
}