01. Day of Week

using System;

namespace DayOfWeek
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] week = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
            int day = int.Parse(Console.ReadLine());

            if (day > 0 && day < 8)
            {
                Console.WriteLine(week[day - 1]);
            }
            else
            {
                Console.WriteLine("Invalid day!");
            }
        }
    }
}

Тарикатско решение:

using System;

namespace DayOfWeek
{
    class Program
    {
        static void Main(string[] args)
        {
            int day = int.Parse(Console.ReadLine());

            Console.WriteLine(day >= 0 && day <= 7 ? new string[]{ "Invalid day!", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"}[day] : "Invalid day!");
        }
    }
}