using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var dayOfWeeks = new List<DayOfWeek>();

        dayOfWeeks.Add(DayOfWeek.Tuesday);

        dayOfWeeks.Add(DayOfWeek.Friday);

        var days = GetAllDayOfWeekPerMonth(DateTime.Now.Month+1, DateTime.Now.Year, dayOfWeeks);

        Console.WriteLine("[\n"+string.Join(",\n", days.Select(x => x.ToString("dd/MM/yyyy")))+"\n]");

    }

​

    public static IEnumerable<DateTime> GetAllDayOfWeekPerMonth(int month, int year, List<DayOfWeek> dayOfWeeks)

    {

        List<DateTime> days = new List<DateTime>();

foreach(DayOfWeek dayOfWeek in dayOfWeeks)

{

    var date = new DateTime(year, month, 1);

    if(date.DayOfWeek != dayOfWeek)

        {

            int daysUntilDayOfWeek = ((int) dayOfWeek - (int) date.DayOfWeek + 7) % 7;

            date = date.AddDays(daysUntilDayOfWeek);

        }

        while(date.Month == month)

        {

            days.Add(date);

            date = date.AddDays(7);         

        }

}

        return days.OrderBy(v=>v);

    }

}