using System;

using System.Text.RegularExpressions;

class Student

{

    public string StudentID;

    public string StudentName;  

    public string _StudentID

    {

        get { return StudentID; }

        set { StudentID=value;  }

    }

    public string _StudentName

    {

        get { return StudentName; }

        set { StudentName=value; }

    }

}

​

class UserDefinedException : ApplicationException

{

    public UserDefinedException()

    {

    }

    //public UserDefinedException(string name):base(String.Format("{0}",name))

   //{

   //}                                                  

}

​

public class Program

{

    public static void Main()

    {

        Student std=null;

        try

        {

            std = new Student();

            std._StudentName="Ridwan";

            Validation(std);

        }

        catch(UserDefinedException ex)

        {

            Console.WriteLine("Invalid Name");

        }

        Console.ReadLine();

    }

     static void Validation(Student stdnt)

    {

        Regex regex =  new Regex("^[a-zA-z]+$");

        if(!regex.IsMatch(stdnt.StudentName))

        throw new UserDefinedException();

    }   

}

​