Get the last Sunday of a month : The Official Microsoft ASP.NET Forums

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Get the last Sunday of a month

Dec 18, 2012 07:11 PM|LINK

Hello all, I've written an extension method that, from a datetime input parameter, gets me the last sunday of the month

public static DateTime LastWeekDayOfTheMonth(this DateTime date, DayOfWeek dayOfWeek) { var day = new DateTime(date.Year, date.Month + 1, 1).AddDays(-1);

while (day.DayOfWeek != dayOfWeek) { day = day.AddDays(-1); }

return day; }

and then I'll call it like:

DateTime LastSundayOfTheMonth = Convert.ToDateTime(MyDate).LastWeekDayOfTheMonth(DayOfWeek.Sunday);

This extension method has a bug if the month is December.

How can I solve this problem?

Luigi

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Re: Get the last Sunday of a month

Dec 18, 2012 07:58 PM|LINK

Change the first line to

var day = new DateTime(date.Year, date.Month, 1).AddMonths(1).AddDays(-1);

Got a c# problem? Try .NET Book Zero from Charles Petzold, it's a free pdf.

Marked as answer by ciupazMI on Dec 19, 2012 07:13 AM

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Re: Get the last Sunday of a month

Dec 19, 2012 04:26 AM|LINK

@ ciupazMI

The .NET Framework makes this easy:

here is a simple test method to show the output:

public static void cwTestResult(DateTime lastDayOfMonth, DateTime lastSunday)
{
    Console.WriteLine("lastDayOfMonth {0}, lastSunday {1}",
       lastDayOfMonth.ToString("yyyy-MMMMM-dd dddd"),
       lastSunday.ToString("yyyy-MMMMM-dd dddd"));
}

first we need to get the last day of the month:

public static Boolean LastDayOfMonth(Int32 year, Int32 month, out DateTime lastDayOfMonth)
{
    Int32 lastDayOfYearMonth;
    try{ lastDayOfYearMonth = DateTime.DaysInMonth(year, month); }
    catch (ArgumentOutOfRangeException badData)
    {
        Console.WriteLine (badData.Message); // .NET error message
        lastDayOfMonth = new DateTime(9999,12,31,23,59,59); // we failed 9999-12-31 23:59:59
        return false;
    }
    lastDayOfMonth = new DateTime(year, month, lastDayOfYearMonth);
    return true;
}

from the last day of the month, getting the last Sunday is easy:

public static DateTime LastSunday(DateTime lastDayOfMonth)
{
    Int32 dayValue = (Int32)lastDayOfMonth.DayOfWeek;
    return lastDayOfMonth.AddDays(-1*dayValue);
}

Here is some code to test this:

void Main()
{
    DateTime lastDayOfMonth;
    DateTime lastSunday;
    if(LastDayOfMonth(2012, 1, out lastDayOfMonth)) // Tuesday
    {
        lastSunday = LastSunday(lastDayOfMonth);
        cwTestResult(lastDayOfMonth, lastSunday);
    }
    if(LastDayOfMonth(2012, 2, out lastDayOfMonth)) // Wednesday
    {
        lastSunday = LastSunday(lastDayOfMonth);
        cwTestResult(lastDayOfMonth, lastSunday);
    }
    if(LastDayOfMonth(2012, 3, out lastDayOfMonth)) // Saturday
    {
        lastSunday = LastSunday(lastDayOfMonth);
        cwTestResult(lastDayOfMonth, lastSunday);
    }
    if(LastDayOfMonth(2012, 12, out lastDayOfMonth)) // Monday
    {
        lastSunday = LastSunday(lastDayOfMonth);
        cwTestResult(lastDayOfMonth, lastSunday);
    }
}

and here is the test output:

lastDayOfMonth 2012-January-31 Tuesday, lastSunday 2012-January-29 Sunday

lastDayOfMonth 2012-February-29 Wednesday, lastSunday 2012-February-26 Sunday

lastDayOfMonth 2012-March-31 Saturday, lastSunday 2012-March-25 Sunday

lastDayOfMonth 2012-December-31 Monday, lastSunday 2012-December-30 Sunday

g.

@ ciupazMI

Note: if you have a valid DateTime, let's name it MyDate, then instead of constants, you would simply write this:

if(LastDayOfMonth(MyDate.Year, MyDate.Month, out lastDayOfMonth)) 
{
    lastSunday = LastSunday(lastDayOfMonth);
    cwTestResult(lastDayOfMonth, lastSunday);
}

g.

B-) Please help me by completing my school survey about computer programmers on my website. Thank you!!! Gerry Lowry +1 705-429-7550 wasaga beach, ontario, canada

Edited by gerrylowry on Dec 19, 2012 04:44 AM
Edited by Mikesdotnetting on Dec 19, 2012 06:56 AM

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Re: Get the last Sunday of a month

Dec 19, 2012 04:44 AM|LINK

Gerry, the code in the original post uses a parameter to determine which weekday is required. So the original code will return the last Tuesday or Friday as required. Your longer, more complex code seems to be hardcoded to Sunday. You could simplify your code by creating an extension method as the original post asked for.

Got a c# problem? Try .NET Book Zero from Charles Petzold, it's a free pdf.

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gerrylowry

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20577 Points

5721 Posts

Re: Get the last Sunday of a month

Dec 19, 2012 05:50 AM|LINK

@ Paul Linton

Hi Paul, based on this comment by the O.P.:

"from a datetime input parameter, gets me the last sunday of the month"

My solution is simple, short and not complex ... given the last day of the month, using existing .NET Framework capabilities, finding the last Sunday requires only two lines and no while loop:

Int32 dayValue = (Int32)lastDayOfMonth.DayOfWeek;
return lastDayOfMonth.AddDays(-1*dayValue);

meanwhile, computing the last day of the month is equally simple; given a year and a month, it simply uses the .DaysInMonth method to construct the end of the month date thanks to this constructor:

http://msdn.microsoft.com/en-us/library/xcfzdy4x.aspx
"DateTime Constructor (Int32, Int32, Int32)"

of course, the LastDayOfMonth looks longer because it allows for error processing.

SHORTER SPECIFIC VERSION -- 4 lines of code

public static DateTime LastSunday(DateTime validDate)
{
    Int32 daysInThisMonth = DateTime.DaysInMonth(validDate.Year, validDate.Month);
    DateTime lastDayOfMonth = new DateTime(validDate.Year, validDate.Month, daysInThisMonth);
    Int32 dayValue = (Int32)lastDayOfMonth.DayOfWeek;
    return lastDayOfMonth.AddDays(-1*dayValue);
}

display method for testing:

public static void cwTestResult(DateTime testDate, DateTime lastSunday)
{
    Console.WriteLine ("lastDayOfMonth {0}, lastSunday {1}", testDate.ToString("yyyy-MMMMM-dd dddd"),  lastSunday.ToString("yyyy-MMMMM-dd dddd"));
}

output from the testing code:

lastDayOfMonth 2012-January-15 Sunday, lastSunday 2012-January-29 Sunday
lastDayOfMonth 2012-February-01 Wednesday, lastSunday 2012-February-26 Sunday
lastDayOfMonth 2012-March-01 Thursday, lastSunday 2012-March-25 Sunday
lastDayOfMonth 2012-December-12 Wednesday, lastSunday 2012-December-30 Sunday

and the code to perform the testing:

void Main()
{
    DateTime testDate;
    DateTime lastSunday;
    
    testDate = new DateTime(2012, 1, 15);
    lastSunday = LastSunday(testDate);
    cwTestResult(testDate, lastSunday);

    testDate = new DateTime(2012, 2, 1);
    lastSunday = LastSunday(testDate);
    cwTestResult(testDate, lastSunday);

    testDate = new DateTime(2012, 3, 1);
    lastSunday = LastSunday(testDate);
    cwTestResult(testDate, lastSunday);

    testDate = new DateTime(2012, 12, 12);
    lastSunday = LastSunday(testDate);
    cwTestResult(testDate, lastSunday);
}

g.

B-) Please help me by completing my school survey about computer programmers on my website. Thank you!!! Gerry Lowry +1 705-429-7550 wasaga beach, ontario, canada

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Paul Linton

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13581 Points

2571 Posts

Re: Get the last Sunday of a month

Dec 19, 2012 05:53 AM|LINK

Paul Linton
Gerry, the code in the original post

Got a c# problem? Try .NET Book Zero from Charles Petzold, it's a free pdf.

Get the last Sunday of a month RSS

5 replies

ciupazMI

Get the last Sunday of a month

Paul Linton

Re: Get the last Sunday of a month

gerrylowry

Re: Get the last Sunday of a month

Paul Linton

Re: Get the last Sunday of a month

gerrylowry

Re: Get the last Sunday of a month

Paul Linton

Re: Get the last Sunday of a month

Paul Linton

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