How do I get the total number of a particular day in a particular month/year?

Let's say i want to know the number of Mondays in Febr开发者_如何学Pythonuary 2014.

I understand this will use the DateTime class, but would like to see some coding examples please.

static int NumberOfParticularDaysInMonth(int year, int month, DayOfWeek dayOfWeek)
{
    DateTime startDate = new DateTime(year, month, 1);
    int totalDays = startDate.AddMonths(1).Subtract(startDate).Days;

    int answer = Enumerable.Range(1, totalDays)
        .Select(item => new DateTime(year, month, item))
        .Where(date => date.DayOfWeek == dayOfWeek)
        .Count();

    return answer;
}

...

int numberOfThursdays = NumberOfParticularDaysInMonth(2010, 9, DayOfWeek.Thursday);

@Anthony has given a nice Linq solution, here is a more traditional implementation.

static int CountDayOfWeekInMonth(int year, int month, DayOfWeek dayOfWeek)
{
  DateTime startDate = new DateTime(year, month, 1);
  int days = DateTime.DaysInMonth(startDate.Year, startDate.Month);
  int weekDayCount = 0;
  for (int day = 0; day < days; ++day)
  {
    weekDayCount += startDate.AddDays(day).DayOfWeek == dayOfWeek ? 1 : 0;        
  }
  return weekDayCount;
}

Used as follows

int numberOfThursdays = CountDayOfWeekInMonth(2014, 2, DayOfWeek.Thursday);  

This one should help you as a start:

How To: Get all Mondays in a given year in C#

You just have to adapt it to use month/year instead of only year.

Solution that almost get what you want:

List the First Monday of every month using C# and VB.NET

Why iterate through the complete month while you can calculate it?

Public Function CountDayOfWeekInMonth(ByVal DateTargeted As Date, Optional ByVal StartingDay As DayOfWeek = DayOfWeek.Sunday) As Integer
    Dim dCountingDate As New DateTime(DateTargeted.Year, DateTargeted.Month, 1)
    Dim iDaysInMonth As Integer = DateTime.DaysInMonth(dCountingDate.Year, dCountingDate.Month)
    Dim iDaysToAdd As Integer = (7 + CType(StartingDay, Integer) - dCountingDate.DayOfWeek) Mod 7
    Dim iFirstStartingDay As Integer = dCountingDate.AddDays(iDaysToAdd).Day
    Return Math.Truncate((iDaysInMonth - iFirstStartingDay) / 7) + 1
End Function

Used as follow

Dim iResult as Integer = CountDayOfWeekInMonth(New DateTime(2012, 04, 30), DayOfWeek.Monday)