using System;

using System.Threading;

public class Program

{

    static readonly string readonlystring;   //you can levae it blank and can assign value at runtime,assign object to it 

    const string constring ="abc"; // you have to assign some value to const while declaring,you can assign ref type to const

    static Program()

    {

        readonlystring ="aaaa"; 

    }

    public static void Main()

    {

        //1. Var vs Dynamic

        var a = "aaaaa";

        //a = 1;   // Cannot implicitly convert type 'int' to 'string'

        dynamic ab = "aaaaa";

        ab =1;

        Console.WriteLine(a.GetType());

        Console.WriteLine(ab.GetType());

        //2. Const and readyonly

        Console.WriteLine(constring);

        Console.WriteLine(readonlystring);

        //3. checked keyword

         int  checkedk = int.MaxValue;

        Console.WriteLine(checkedk);

        Console.WriteLine((checkedk+ 20) + " is a wrong output to handle such situation use checked keyword" );

        //uncomment below code to throw error

        //checked block

        //Console.WriteLine(checked(checkedk+ 20));

        //checked expression

            //checked

            //{

            //  int i = 10;

            //   int i3 = 2147483647 + i;

              //  Console.WriteLine(i3);

            //}

        //4 . as and is keyword

        person p = new person();

        Men men = new Men();

        Men m2 =  p as Men;

        Console.WriteLine(p is Men);

        Console.WriteLine(men is person);

        if(m2 !=null)

        {

            Console.WriteLine("m is person type");

        }

        else

        {

           Console.WriteLine("m is not person type");

        }

    }

        public class person

        {

            public string Fname{get;set;}

            public string Lname{get;set;}

        }

        public class Men : person

        {

            public string Fisrtname{get;set;}

            public string Lastname{get;set;}

        }

}