static constructors

Static constructor is used to initialize static variables defined in a class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication6
{   
    class Program
    {
        static int num;
        int a = 10;
        static Program()
        {
            num = 10;
        //    a = 40; this is error
        }

        

        public Program()
        {

        }
        public Program( int num )
        {
           Console.WriteLine(num);
        }

        static void Main(string[] args)
        {
            Program p1,p2,p3;
            p1 = new Program(10);
            p2 = new Program(10);
            p3 = new Program(10);

            Program obj = new Program();
        }        
        
    }
}


////////////////
// Static constructor - Another example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Drawing;


namespace ConsoleApplication6
{   
    class Program
    {
        public static readonly Color BackColor;

        static Program()
        {
            DateTime now = DateTime.Now;

            if (now.DayOfWeek == DayOfWeek.Saturday ||
                now.DayOfWeek == DayOfWeek.Sunday)
            {
                BackColor = Color.Green;
            }
            else
            { 
                BackColor = Color.Red;
            }
        }
         
        static void Main(string[] args)
        {
            Console.WriteLine(@"User-preferences: BackColor is: 
                " + Program.BackColor.ToString());
        }        
        
    }
}