using System;

public class Person{

        public int Age;

        public Person(){

    Age=10;  // default constructor with value of age initially as 10 years.

        }

        public void SetAge (int n){

            Age = n;     // Person class with method SetAge (int n)

        }

        public void SetAge (int n,int p){

            Age = n+p;  //person class with overload method "SetAge (int n, int p)"

        }

        public void SayHello (){

            Console.WriteLine("Hello");

        }

    }

​

    public class Student: Person{                       //derived student class from person

        public void ShowAge(){

            Console.WriteLine("My age is: {0} years old",this.Age);

        }

        public void GoToClasses(){

            Console.WriteLine("I’m going to class.");

        }   //"Student" with public method "GoToClasses", which will write on screen "I’m going to class."

    }

​

    public class Teacher: Person{                  //derived student class from person

​

        private string subject;  //private attribute subject

        public void Explain(){

            Console.WriteLine("Explanation begins");

        }   //Teacher with a public method Explain()

    }

​

public class StudentAndTeacherTest

{

    public static void Main()

    {

        Person p1 = new Person();  //object of person

        p1.SayHello();

        Console.WriteLine(p1.Age); //value of default constructor

        Student s1=new Student();  //object of student created

        s1.SetAge(21);

                             s1.SayHello();

        s1.ShowAge();

        s1.SetAge(21,51);

                             s1.SayHello();

        s1.ShowAge();

        Teacher t1=new Teacher(); //object of teacher created

        t1.SetAge(30);

        t1.SayHello();

        t1.Explain();

        }      }

​