### Задача 5 на множества из учебника
```
   SortedSet<int> one = new SortedSet<int>();
    SortedSet<int> two = new SortedSet<int>();
    SortedSet<int> three = new SortedSet<int>();
    Console.Write("Числа в множестве(от и до): ");
    string[] interval = Console.ReadLine().Split(" ");
    
    for (int i = Convert.ToInt32(interval[0]); i <= Convert.ToInt32(interval[1]); i++)
    {
        one.Add(i);
    }

    foreach (var a in one)
    {
        if (IsSimple(a))
        {
            two.Add(a);
        }
        else
        {
            three.Add(a);
        }
    }
    
    ShowColl(two,"Составные числа: ");
    ShowColl(three,"Простые числа: ");
    

static bool IsSimple(int a)
{
    int b = Convert.ToInt32(Math.Sqrt(a));
    for (int i = 2; i <= b; i++)
    {
        if (a % i == 0)
        {
            return false;
        }
    }
    
    return true;
}

static void ShowColl(SortedSet<int> numbers, string a)
{
    Console.Write(a);
    foreach (var b in numbers)
    {
        Console.Write(b + " ");
    }
    
    Console.WriteLine();
}
```

### 1
```
while (true)
{
    Console.Write("date(dd.mm.yyyy): ");
    try
    {
        DateTime date = Convert.ToDateTime(Console.ReadLine());
        Console.WriteLine("date is correct");
    }
    catch (Exception)
    {
        Console.WriteLine("wrong date");
    }
}
```

### 2
```
while (true)
{
    Console.Write("first date: ");
    DateTime date1 = Convert.ToDateTime(Console.ReadLine());
    Console.Write("second date: ");
    DateTime date2 = Convert.ToDateTime(Console.ReadLine());
    Console.WriteLine("days: {0}", date1.Subtract(date2).TotalDays);
}
```

### 3
```
while (true)
{
    Console.Write("first date: ");
    DateTime date1 = Convert.ToDateTime(Console.ReadLine());
    Console.Write("second date: ");
    DateTime date2 = Convert.ToDateTime(Console.ReadLine());
    Console.WriteLine("hours: {0}", date1.Subtract(date2).TotalHours);
}
```

### 4
```
while (true)
{
    Console.Write("first date: ");
    DateTime date1 = Convert.ToDateTime(Console.ReadLine());
    Console.Write("second date: ");
    DateTime date2 = Convert.ToDateTime(Console.ReadLine());
    Console.WriteLine("minutes: {0}", date1.Subtract(date2).TotalMinutes);
}
```

### 5
```
while (true)
{
    Console.Write("year: ");
    int year = int.Parse(Console.ReadLine());
    DateTime date1 = new DateTime(year, 01, 01);
    double day = 256 - date1.DayOfYear;
    date1 = date1.AddDays(day);
    Console.WriteLine("date: {0} day of week: {1}", date1.ToShortDateString(), date1.DayOfWeek);
}
```

### 6
```
while (true)
{
    DateTime date1 = DateTime.Now;
    Console.Write("day: ");
    double day = Convert.ToDouble(Console.ReadLine());
    if (day > date1.DayOfYear)
        date1 = date1.AddDays(day - date1.DayOfYear);
    else
        date1 = date1.AddDays(-(date1.DayOfYear - day));
    Console.WriteLine("day of week: {0}", date1.DayOfWeek);
}
```

### 7
```
while (true)
{
    DateTime date1 = new DateTime(2024, 5, 23);
    Console.Write("Дата: ");
    DateTime date2 = Convert.ToDateTime(Console.ReadLine());
    if (date1 > date2)
        Console.WriteLine("До экзамена: {0} дней",date1.Subtract(date2).TotalDays);
    else if (date1 < date2)
        Console.WriteLine("Со дня экзамена прошло: {0} дней", date2.Subtract(date1).TotalDays);
    else
        Console.WriteLine("Экзамен сегодня!");
}
```

### 8
```
DateTime date = DateTime.Now;
Console.WriteLine(date.AddDays(1).ToShortDateString());
```

### 9
```
while(true)
{
    Console.Write("День рождения(дд.мм.гггг): ");
    string[] ddmm = Console.ReadLine().Split('.');
    DateTime dob = new DateTime(2024, int.Parse(ddmm[1]), int.Parse(ddmm[0]));
    DateTime date = DateTime.Now;
    if (dob > date)
        Console.WriteLine("До дня рождения {0} дней", Convert.ToInt32(dob.Subtract(date).TotalDays) );
    else if (dob < date)
        Console.WriteLine("Со дня рождения прошло {0} дней", Convert.ToInt32(date.Subtract(dob).TotalDays));
    else
        Console.WriteLine("С днем рождения!");
}
```

### 10
```
Console.Write("Введите время на часах: ");
string[] time = Console.ReadLine().Split(':');
DateTime date1 = DateTime.Today;
date1 = date1.AddHours(double.Parse(time[0])).AddMinutes(double.Parse(time[1])).AddSeconds(double.Parse(time[2]));
Console.WriteLine("С начала суток прошло: {0} секунд",Convert.ToInt32(date1.Subtract(DateTime.Today).TotalSeconds));
```

### 11
```
Console.Write("Введите количество дат: ");
int a = int.Parse(Console.ReadLine());
List<DateTime> dates = new List<DateTime>();
DateTime today = DateTime.Today;
for (int i = 0; i < a; i++)
{
    Console.Write("Введите {0} дату: ", i+1);
    dates.Add(Convert.ToDateTime(Console.ReadLine()));
}

double difference = Math.Abs(today.Subtract(dates[0]).TotalDays);
DateTime datean = new DateTime();
foreach (var date in dates)
{
    double days = Math.Abs(today.Subtract(date).TotalDays);
    if (days < difference)
    {
        difference = days;
        datean = date;
    }
}
Console.WriteLine("Ближайшая дата: {0}",datean.ToShortDateString());
```

### 12
```
Console.Write("Введите количество дат: ");
int a = int.Parse(Console.ReadLine());
List<DateTime> dates = new List<DateTime>();
DateTime today = DateTime.Today;
for (int i = 0; i < a; i++)
{
    Console.Write("Введите {0} дату дня рождения: ", i+1);
    dates.Add(Convert.ToDateTime(Console.ReadLine()));
}

List<int> months = new List<int>();
foreach (var date in dates)
{
    if (months.IndexOf(date.Month) == -1)
    {
        months.Add(date.Month);
    }
}

foreach (var month in months)
{
    int count = 0;
    Console.Write("Дней рождений в {0} месяце: ", month);
    foreach (var date in dates)
    {
        if (date.Month  == month)
        {
            count++;
        }
    }
    Console.Write(count);
    Console.WriteLine();
}
```

### 13
```
string [] dates = {"12.02.2005", "13.05.2005", "15.09.2014", "23.02.2019", "19.02.2001","30.09.2010"};
Dictionary<int, int> months = new Dictionary<int, int>();
foreach (var date in dates)
{
    DateTime datec = DateTime.Parse(date);
    if (months.ContainsKey(datec.Month))
    {
        months[datec.Month]++;
    }
    else
    {
        months.Add(datec.Month, 1);
    }
}

int a = 0;
int b = 0;
foreach (var month in months)
{
    if (month.Value > a)
    {
        a = month.Value;
        b = month.Key;
    }
}
Console.WriteLine($"{b} месяц самый популярный.");
```

### 14
```
Console.WriteLine("Понедельник: " + (double)Counter(DayOfWeek.Monday) / 50*12);
Console.WriteLine("Вторник: " + (double)Counter(DayOfWeek.Tuesday) / 50*12);
Console.WriteLine("Среда: " + (double)Counter(DayOfWeek.Wednesday) / 50*12);
Console.WriteLine("Четверг: " + (double)Counter(DayOfWeek.Thursday) / 50*12);
Console.WriteLine("Пятница: " + (double)Counter(DayOfWeek.Friday) / 50*12);
Console.WriteLine("Суббота: " + (double)Counter(DayOfWeek.Saturday) / 50*12);
Console.WriteLine("Воскресенье: " + (double)Counter(DayOfWeek.Sunday) / 50*12);
static int Counter(DayOfWeek day)
{
    int count = 0;
    for (int year = 1; year <= 50; year++)
    {
        for (int month = 1; month < 12; month++)
        {
            DateTime date = new DateTime(year, month, 13);
            if (date.DayOfWeek == day)
            { 
                count++;
            }
        }
    }

    return count;
}
```

### 15
```
Console.Write("year: ");
int year = int.Parse(Console.ReadLine());
DateTime date1 = new DateTime(year, 1, 1);
DateTime date2 = new DateTime(year, 12, 31);
Console.WriteLine(holidays(date1,date2));
static int holidays (DateTime date1, DateTime date2)
{
    int days = 0;
    for (var a = date1; a < date2; a.AddDays(1))
    {
        if (a.DayOfWeek == DayOfWeek.Saturday || a.DayOfWeek == DayOfWeek.Sunday)
        {
            days++;
        }
    }

    return days;
}
```