C# 根据年月获得此月第一天和最后一天，并计算工作日

string str = "2015年3月";

int firstIndex = str.IndexOf("年", );

int secondIndex = str.IndexOf("月", firstIndex + );

string month = str.Substring(firstIndex + , secondIndex - firstIndex - );

string year = str.Substring(, );

DateTime dt = DateTime.Now;

string[] time = dt.ToString().Split(new char[]{'/'});

string date = year + "/" + month + "/" + time[];

DateTime first = Convert.ToDateTime(date).AddDays( - Convert.ToDateTime(date).Day);

DateTime last=Convert.ToDateTime(date).AddDays( - Convert.ToDateTime(date).Day).AddMonths().AddDays(-);

//The first day of the month

Label1.Text = first.ToString();

//The last day of the month

Label2.Text = last.ToString();

//businessDays of the month(except on the weekend)

Label3.Text = getint(first, last).ToString();

public int getint(DateTime firstDay, DateTime lastDay)

{

    firstDay = firstDay.Date;

    lastDay = lastDay.Date;

    if (firstDay > lastDay)

        throw new ArgumentException("Incorrect last day " + lastDay);

    TimeSpan span = lastDay - firstDay;

    int businessDays = span.Days + ;

    int fullWeekCount = businessDays / ;

    // find out if there are weekends during the time exceedng the full weeks

    if (businessDays > fullWeekCount * )

    {

        // we are here to find out if there is a 1-day or 2-days weekend

        // in the time interval remaining after subtracting the complete weeks

        int firstDayOfWeek = firstDay.DayOfWeek == DayOfWeek.Sunday ?  : (int)firstDay.DayOfWeek;

        int lastDayOfWeek = lastDay.DayOfWeek == DayOfWeek.Sunday ?  : (int)lastDay.DayOfWeek;

        if (lastDayOfWeek < firstDayOfWeek)

            lastDayOfWeek += ;

        if (firstDayOfWeek <= )

        {

            if (lastDayOfWeek >= )// Both Saturday and Sunday are in the remaining time interval

                businessDays -= ;

            else if (lastDayOfWeek >= )// Only Saturday is in the remaining time interval

                businessDays -= ;

        }

        else if (firstDayOfWeek <=  && lastDayOfWeek >= )// Only Sunday is in the remaining time interval

            businessDays -= ;

    }

    // subtract the weekends during the full weeks in the interval

    businessDays -= fullWeekCount + fullWeekCount;

    return businessDays;

}