using System;

​

public class Program

{

    public static void Main(string[] args)

    {

        Guest g1 = new Guest("X", "Seabi", 30);

        try 

            {

                Guest.ValidateGuest(g1);

            }

            catch (InvalidNameException ine) when (g1.FirstName != "J") 

            {

                Console.WriteLine(ine.Message);

            }

            catch(InvalidNameException ine ){

                Console.WriteLine(ine.Message + ": Not J");

            }

        //the 'when' clause is usefule for when you wwant to handle an exception based on the 

        //exception type / code

        //it does not harm the stact trace, hence it is a proper way of handling excpetions

    }

}

​

public class InvalidNameException : Exception

    {

        public InvalidNameException() { }

        public InvalidNameException(string name) : base (string.Format("Invalid guest name {0}", name)) { }

    }

    class Guest

    {

        public string FirstName;

        private string LastName;

        private int Age;

        //the 'throw' keyword is used to manually raise exceptions that inherit from the Exception class

        //since all exceptions derive from the Exception class, then all exceptions can be invoked manually

        //using the throw keyword

        public Guest(string fName, string lName, int age)

        {

            FirstName = fName;

            LastName = lName;

            if (age < 21)

                throw new ArgumentOutOfRangeException("age","All guests must be 21-years-old or older.");

            Age = age;

        }

        public string GuestInfo()

        {

            string gInfo = FirstName + " " + LastName + ", " + Age.ToString();

            return(gInfo);

        }

        public static void ValidateGuest(Guest g){

            //name atleast two charecters

            if(g.FirstName.Length < 2)

                throw new InvalidNameException(g.FirstName);

        }

    }