using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 13; i <= 31; i++)
            {
                DateTime start = new DateTime(2014, 10, i);
                DateTime stop = new DateTime(2014, 10, 31);

                int totalWorkingDays = GetNumberOfWorkingDays(start, stop);

                Console.WriteLine("There are {1} working days from Oct {0}, 2014 to Oct 31, 2014.", i, totalWorkingDays);
            }
        }

        private static int GetNumberOfWorkingDays(DateTime start, DateTime stop)
        {
            TimeSpan interval = stop - start;

            int totalWeek = interval.Days / 7;
            int totalWorkingDays = 5 * totalWeek;

            int remainingDays = interval.Days % 7;


            for (int i = 0; i <= remainingDays; i++)
            {
                DayOfWeek test = (DayOfWeek)(((int)start.DayOfWeek + i) % 7);
                if (test >= DayOfWeek.Monday && test <= DayOfWeek.Friday)
                    totalWorkingDays++;
            }

            return totalWorkingDays;
        }
    }
}

private static int GetNumberOfWorkingDaysJeroen(DateTime start, DateTime stop)
{
    int days = 0;
    while(start <= stop)
    {
        if(start.DayOfWeek != DayOfWeek.Saturday && start.DayOfWeek != DayOfWeek.Sunday)
        {
            ++days;
        }
        start = start.AddDays(1);
    }
    return days;
}

private static int GetNumberOfWorkingDays(DateTime start, DateTime stop)
    {
        var days = (stop - start).Days + 1;
        return workDaysInFullWeeks(days) + workDaysInPartialWeek(start.DayOfWeek, days);
    }

    private static int workDaysInFullWeeks(int totalDays)
    {
        return (totalDays / 7) * 5;
    }

    private static int workDaysInPartialWeek(DayOfWeek firstDay, int totalDays)
    {
        var remainingDays = totalDays % 7;
        var daysToSaturday = (int) DayOfWeek.Saturday - (int) firstDay;
        if(remainingDays <= daysToSaturday)
            return remainingDays;
        /* daysToSaturday are the days before the weekend,
         * the rest of the expression computes the days remaining after we
         * ignore Saturday and Sunday
         */
        // Range ends in a Saturday or in a Sunday
        if (remainingDays <= daysToSaturday + 2)
            return daysToSaturday;
        // Range ends after a Sunday
        else
            return remainingDays - 2;
    }

namespace Extensions{
    using System;
    public static class DateTimeExtensions {
        public static int GetNumberOfWeekDays(this DateTime dateTime, DateTime end_date_time){
            int days = 0;
            while(dateTime <= end_date_time)   {
                if(dateTime.DayOfWeek != DayOfWeek.Saturday && // IF not sat
                    dateTime.DayOfWeek != DayOfWeek.Sunday)    // And not sunday
                    ++days;
                dateTime = dateTime.AddDays(1);
            }
            return days;
        }

        public static DateTime AddWeekDays(this DateTime dateTime, int days) =>
             dateTime.AddDays(dateTime.GetNumberOfWeekDays(dateTime.AddDays(days)));
    }
}

namespace ConsoleApplication1 {
    using System;
    using static Extensions.DateTimeExtensions;
    class Program  {
        static void Main(string[] args) {

          DateTime date = DateTime.Now;

          // Example usage of Get Number of weekdays
          int weekDays = date.GetNumberOfWeekDays(dateTime.AddDays(10))

          // Example usage of Add Week Days
          DateTime endDate = date.AddWeekDays(4);

        }
    }
}

public int GetWorkingDays(DateTime from, DateTime to)
{
var totalDays = 0;
for (var date = from; date < to; date = date.AddDays(1))
{
    if (date.DayOfWeek != DayOfWeek.Saturday
        && date.DayOfWeek != DayOfWeek.Sunday)
        totalDays++;
}

return totalDays;
}