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How to know how many times it was the first day of the month in a time frame in C# [closed]

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Say I have a timeframe defined by two DateTime objects, d1 and d2.
How could I know the number of times the first day of a month is in the timeframe?

You could something like:
DateTime startDate = DateTime.Now.AddDays(-100); // {18/11/2014 4:04:07 PM}
DateTime endDate = DateTime.Now; // {26/02/2015 4:04:07 PM}
var query = Enumerable.Range(0, 1 + (endDate - startDate).Days)
.Select(i => startDate.AddDays(i))
.Where(r=> r.Day == 1);
This will first create a collection of dates from start to end, and later you can filter the results where Day part is 1.
For output:
foreach (var dateTime in query)
{
Console.WriteLine(dateTime);
}
Output:
01/12/2014 4:04:07 PM
01/01/2015 4:04:07 PM
01/02/2015 4:04:07 PM

Another approach without the previous bruit force....
DateTime startDate = new DateTime(2014, 09, 01);
DateTime endDate = new DateTime(2015, 02, 02);
DateTime loopDate = startDate;
var totalMonths = ((endDate.Year - startDate.Year) * 12) + endDate.Month - startDate.Month;
if (startDate.Day != 1)
{
loopDate = new DateTime(startDate.Year, startDate.Month, 1).AddMonths(1);
}
List<DateTime> firstDayOfMonth = Enumerable.Range(0, totalMonths)
.Select(i => loopDate.AddMonths(i))
.ToList();
firstDayOfMonth.Add(new DateTime(endDate.Year,endDate.Month, 1));
This calculates the months difference based on solution provided here. Later it checks if the startDate is the first day of month then ignore it, and creates a loopDate which would be next available first day of month, and continues till endDate.
Here is a working .Net fiddle

This is simple math.
D1: Jan 23rd 2015
D2: Mar 2nd 2015
Find the number of months that have passed (d2.Month - d1.Month).
That gives you the number of first of the months that have passed.
Edge cases you will need to consider:
D1 is the first day of the month - just do a simple check for that
and add 1 to the result
D1 and D2 year is different - this is simple as well:
2.1. Calculate months between D1 and the end of its year (IE: D1 to
Dec 31st), then make sure to check edge case 1.
2.2. Calculate the months between D2 and the start of its year (IE: Jan 1st to D2)
2.3. After that, add 12 for every year difference greater than 1 (it
means more than one year has passed - D1 is 2010 and D2 is 2013 - 2
whole years have passed. Step one caclulated the months in 2010,
and step 2 for 2013.
2.4. Add the results of steps 1,2, and 3
together.

How to get date after N months with same day and same week of a given date

I am looking for some logic to get the date after N months having same day(Ex:Wednesday) and same week(ex: first or second...) of a given date.
ex: 12-06-2013(Wednesday & 3rd week of June) is the given date.
here I am adding 3 months to the given date.
the result should be is 14-Aug-2013(Wednesday & 3rd week of Aug).
please let me know if you need more clarification.
Thanks In advance.

Okay, so I'd personally use my Noda Time library to do this. It's entirely possible to do this with DateTime, but I'd personally find it harder. I'd also encourage you to use Noda Time in general, of course, as a better date/time API. So I'd have something like:
static LocalDate AddMonthsPreserveWeekDayAndWeek(LocalDate start, int months)
{
// This isn't the week of month in the "normal" sense; it's the nth
// occurrence of this weekday.
int week = ((start.DayOfMonth - 1) / 7) + 1;
// This will usually give the same day of month, but truncating where
// necessary
LocalDate monthsAdded = start.AddMonths(months);
LocalDate endOfPreviousMonth = monthsAdded.AddDays(-monthsAdded.Day);
// Get to the first occurrence of the right day-of-week
LocalDate firstRightDay = endOfPreviousMonth.Next(start.IsoDayOfWeek);
// Usually this will be right - but it might overflow to the next month,
// in which case we can just rewind by a week.
LocalDate candidate = firstRightDay.PlusWeeks(week - 1);
return candidate.Month == firstRightDay.Month ? candidate
: candidate.PlusWeeks(-1);
}
This is completely untested though - you should absolutely have a bunch of unit tests (ideally which you write before even including this code) which test all kinds of edge cases you're interested in.

Using standard MDSN year = 2013 month = 06 date = 12
1) Get day of the week from the specific date (Sunday is 0)
DateTime dateValue = new DateTime(year, month, date);
Console.WriteLine((int) dateValue.DayOfWeek); // Displays 3 implying it is Wed
2) Get the week of the month from the specific date
DayofWeek = 3 (from previous calculation)
Day = 12
EndOfWeek = Day + (6 - DayOfWeek) = 12 + 4 = 16
NoWeek = 0
while (EndOfWeek > 0)
{
EndOfWeek -= 7;
NoWeek++;
}
=> NoWeek = 3
3) Get first date after N month
DateTime newDate = new DateTime(year, month, 1)
newDate.AddMonths(N); // Let it be 2 => August 1, 2013
4) Get the day of the week for the new date
newDay = newDate.DayOfWeek // Return 4 implying Thursday
5) Get the last day after NoWeek
newDate.AddDays(6-newDay) => newDate.AddDays (6-4) => August 3,2013
NoWeek--;
while (NoWeek > 1)
{
newDate.AddDays(7);
NoWeek--;
}
=> newDate will be Augus 10,2013
6) Calculte required date
newDate.AddDays(DayofWeek) =>newDate will be August 14,2013

ASP.NET Getting working weeks for every month

I have a form that accept input of 'Month' and 'Year', I am writing here to ask any idea on how will I get all 'working weeks'?
I mean 'Working weeks' as Monday - Friday
So basically I need week1 to week4 or if available including week5.
For example if I input January 2013:
week1 = January 1 to January 4
week2 = January 7 to January 11
week3 = January 14 to January 18
week4 = January 21 to January 25
week5 = January 28 to January 31
How can I achieve that? Thanks for any help! Any suggestions or ideas will be greatly appreciated. Thanks mates! :)

You could use this Linq query:
int month = 1;
int year = 2013;
var cal = System.Globalization.CultureInfo.CurrentCulture.Calendar;
IEnumerable<int> daysInMonth = Enumerable.Range(1, cal.GetDaysInMonth(year, month));
List<Tuple<int, DateTime, DateTime>> listOfWorkWeeks = daysInMonth
.Select(day => new DateTime(year, month, day))
.GroupBy(d => cal.GetWeekOfYear(d, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday))
.Select(g => Tuple.Create(g.Key, g.First(), g.Last(d => d.DayOfWeek != DayOfWeek.Saturday && d.DayOfWeek != DayOfWeek.Sunday)))
.ToList();
// Item1 = week in year, Item2 = first day, Item3 = last working day
int weekNum = 1;
foreach (var weekGroup in listOfWorkWeeks)
{
Console.WriteLine("Week{0} = {1} {2} to {1} {3}"
, weekNum++
, System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(month)
, weekGroup.Item2.Day
, weekGroup.Item3.Day);
}
output for January:
Week1 = January 1 to January 4
Week2 = January 7 to January 11
Week3 = January 14 to January 18
Week4 = January 21 to January 25
Week5 = January 28 to January 31
and for February:
Week1 = February 1 to February 1
Week2 = February 4 to February 8
Week3 = February 11 to February 15
Week4 = February 18 to February 22
Week5 = February 25 to February 28

Find the first Monday of the month and year.
int year = 2013;
int month = 1;
DateTime testDate = new DateTime(year,month,1);
while ( testDate.DayOfWeek != DayOfWeek.Monday )
{
testDate = testDate.AddDays(1);
}
Then iterate over each week until you reach a year that isn't 2013.
// Should have first monday now.
// Loop until the month changes
while ( testDate.Month == month)
{
var monday = testDate;
var friday = testDate.AddDays(4);
// You now have both dates. Do whatever you need to.
// here.
// Increment test date by a week
testDate = testDate.AddDays(7)
}

In pseudo code:
Start from the first day of the month
While (day != Monday) take next date (+1 day)
See this SO post (Jon Skeet answer!) for checking if a day is a Monday.
Add 4 days to find the end of the working week
If it's in the same month, than you have a working week for your answer.
Add 7 days to find the next Monday
If the new Monday is still within the same month: repeat 3. and 4.
EDIT The above finds all complete working weeks.
To find the other weeks as well:
If the first day of the month is already a working day, find the next Friday. -> 1st working week
If the last friday is in the next month, finish the last working week at the last day of the month. -> last working week

Week of Year C# Datetime

I have following code to get the weeknumber of the year given in the DateTime object Time
public static int WeeksInYear(DateTime date)
{
GregorianCalendar cal = new GregorianCalendar(GregorianCalendarTypes.Localized);
return cal.GetWeekOfYear(date, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}
I give the function the date 1/1/2012 which should return week 1, but it is returning week 52. And I can't seem to figure out why. Anyone have an idea why?

The algorithm is doing exactly what you have instructed it to do. You have the CalanderWeekRule set to FirstFourDayWeek. The 1st of January 2012 was not part of the first four day week, so you have instructed the calander to start counting from January 2nd.
Calculate date from week number

public static int WeeksInYear(DateTime date)
{
GregorianCalendar cal = new GregorianCalendar(GregorianCalendarTypes.Localized);
return cal.GetWeekOfYear(date, CalendarWeekRule.FirstDay, DayOfWeek.Monday);
I think if change CalendarWeekRule.FirstFourDayWeek to CalendarWeekRule.FirstDay then this will work fine.
I changed this then its working fine.

The weeknumber was correctly calculated. You should have a read on how weeknumbers are actually calculated/counted (Wikipedia?!).
Attention: The built-in calculation of week-number-calculation is buggy. Microsoft describes the problem in the KnowledgeBase-Article 200299. It has problems with ISO-8601.

You can use the class Week of the Time Period Library for .NET which supports supports the ISO 8601 week numbering:
TimeCalendar calendar = new TimeCalendar(
new TimeCalendarConfig { YearWeekType = YearWeekType.Iso8601 } );
Week week = new Week( new DateTime( 2012, 01, 01 ), calendar );
Console.WriteLine( "week #: ", week.WeekOfYear );

I assume that because 1/1/2012 was a Sunday and GetWeekOfYear says it returns the week which includes the date, it's returning the last week of 2011 rather than the first week of 2012.
Have a look at the CalendarRule for clarification.

1/1/2012 it was sunday. I believe that's why you get 52, because it was last day of the last year week. For the 2nd of january you should get the right result.

Calculate DateTime Weeks into Rows

I am currently writing a small calendar in ASP.Net C#. Currently to produce the rows of the weeks I do the following for loop:
var iWeeks = 6;
for (int w = 0; w < iWeeks; w++) {
This works fine, however, some month will only have 5 weeks and in some rare cases, 4.
How can I calculate the number of rows that will be required for a particular month?
This is an example of what I am creating:
As you can see for the above month, there are only 5 rows required, however. Take the this month (August 2008) which started on a Saturday and ends on a Monday on the 6th Week/Row.
Image found on google
This is an example of what I am creating:
As you can see for the above month, there are only 5 rows required, however. Take the this month (August 2008) which started on a Saturday and ends on a Monday on the 6th Week/Row.
Image found on google

Here is the method that does it:
public int GetWeekRows(int year, int month)
{
DateTime firstDayOfMonth = new DateTime(year, month, 1);
DateTime lastDayOfMonth = new DateTime(year, month, 1).AddMonths(1).AddDays(-1);
System.Globalization.Calendar calendar = System.Threading.Thread.CurrentThread.CurrentCulture.Calendar;
int lastWeek = calendar.GetWeekOfYear(lastDayOfMonth, System.Globalization.CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
int firstWeek = calendar.GetWeekOfYear(firstDayOfMonth, System.Globalization.CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
return lastWeek - firstWeek + 1;
}
You can customize the calendar week rule by modifying the System.Globalization.CalendarWeekRule.FirstFourDayWeek part. I hope the code is self explanatory.

Well, it depends on the culture you're using, but let's assume you can use Thread.CurrentThread.CurrentCulture, then the code to get the week of today would be:
Culture culture = Thread.CurrentThread.CurrentCulture;
Calendar cal = culture.Calendar;
Int32 week = cal.GetWeekOfYear(DateTime.Today,
culture.DateTimeFormat.CalendarWeekRule,
culture.DateTimeFormat.FirstDayOfWeek);

How about checking which week the first and last days will be in?

you can get the days of a month by using DateTime.DaysInMonth(int WhichYear,int WhichMonth);

The months in the Julian / Gregorian calendar have the same number of days each year, except February who can have 28 or 29 days depending on the leapness of the year. You can find the number of days in the Description section at http://en.wikipedia.org/wiki/Gregorian_calendar.
As #darkdog mentioned you have DateTime.DaysInMonth. Just do this:
var days = DateTime.DaysInMonth(year, month) +
WhatDayOfWeekTheMonthStarts(year, month);
int rows = (days / 7);
if (0 < days % 7)
{
++rows;
}
Take into consideration the fact that for globalization / localization purposes, some parts of the world use different calendars / methods of organization of the year.

The problem isn't the number of days in the month, it's how many weeks it spans over.
February in a non-leap year will have 28 days, and if the first day of the month is a monday, february will span exactly 4 week numbers.
However, if the first day of the month is a tuesday, or any other day of the week, february will span 5 week numbers.
A 31 day month can span 5 or 6 weeks the same way. If the month starts on a monday, the 31 days gives you 5 week numbers. If the month starts on saturday or sunday, it will span 6 week numbers.
So the right way to obtain this number is to find the week number of the first and last days of the month.
Edit #1: Here's how to calculate the number of weeks a given month spans:
Edit #2: Fixed bugs in code
public static Int32 GetWeekForDateCurrentCulture(DateTime dt)
{
CultureInfo culture = Thread.CurrentThread.CurrentCulture;
Calendar cal = culture.Calendar;
return cal.GetWeekOfYear(dt,
culture.DateTimeFormat.CalendarWeekRule,
culture.DateTimeFormat.FirstDayOfWeek);
}
public static Int32 GetWeekSpanCountForMonth(DateTime dt)
{
DateTime firstDayInMonth = new DateTime(dt.Year, dt.Month, 1);
DateTime lastDayInMonth = firstDayInMonth.AddMonths(1).AddDays(-1);
return
GetWeekForDateCurrentCulture(lastDayInMonth)
- GetWeekForDateCurrentCulture(firstDayInMonth)
+ 1;
}

Try this,
DateTime.DaysInMonth

First Find out which weekday the first day of the month is in. Just new up a datetime with the first day, always 1, and the year and month in question, there is a day of week property on it.
Then from here, you can use the number of days in the month, DateTime.DaysInMonth, in order to determine how many weeks when you divide by seven and then add the number of days from 1 that your first day falls on. For instance,
public static int RowsForMonth(int month, int year)
{
DateTime first = new DateTime(year, month, 1);
//number of days pushed beyond monday this one sits
int offset = ((int)first.DayOfWeek) - 1;
int actualdays = DateTime.DaysInMonth(month, year) + offset;
decimal rows = (actualdays / 7);
if ((rows - ((int)rows)) > .1)
{
rows++;
}
return rows;
}

Check Calendar.GetWeekOfYear. It should do the trick.
There is a problem with it, it does not follow the 4 day rule by ISO 8601, but otherwise it is neat.