FindNthOccurenceOfWeekDayForMonth

FindNthOccurenceOfWeekDayForMonth.cs

public DateTime FindNthOccurenceOfWeekDayForMonth(int month, int year, DayOfWeek weekDay, int occurence)
{
	if(occurence < 1)
	{
		throw new ArgumentOutOfRangeException("occurence must be greater than 0");
	}
	
	// iterate over days, beginning with the first day of the given month and year
	// loop until occurence = 0
	// when loop exits current will be set to the nth occurence of weekDay 
	var current = new DateTime(year, month, 1);		
	while(true)
	{
		if(current.DayOfWeek == weekDay) occurence--;				
		if(occurence == 0) break;		
		current = current.AddDays(1);		
	}
	
	if(current.Month != month) 
	{
		throw new ArgumentOutOfRangeException("occurence for week day falls outside of given month");
	}
	return current;
}