DemoOOP

// Клас Student

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.NetworkInformation;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Linq;

namespace DemoOOP
{
    public class Student : Person
    {
        // Полета - Състояние
        private int Pin;
        private string Name;
        private string LastName;
        private double gradeBEL;

        public Student(int Pin, string Name, string LastName, double grade) : base(Pin, Name, LastName)
        {
            this.Pin = Pin;
            this.Name = Name;
            this.LastName = LastName;
            this.gradeBEL = grade;
        }

        // ctor с параметри)



        // Метод за изчисляване на средна оценка по два предмета
        public double CalcAvgGrade(double grade1, double grade2)
        {
            double avg = (grade1 + grade2)/2;


            return avg;
        }

        // Метод за принтиране данните на обект в конзолата
        public void PrintData()
        {
            Console.WriteLine(this.Pin);
            Console.WriteLine(this.Name);
            Console.WriteLine(this.LastName);
            Console.WriteLine(this.gradeBEL);
        }

    }
}

//==============================================

Клас Person

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

namespace DemoOOP
{
    public class Person
    {

        private int Pin;
        private string Name;
        private string LastName;


        public Person( int Pin,  string Name, string LastName)
        {
            this.Pin = Pin;
            this.Name = Name;
            this.LastName = LastName;
        }
    }
}


//================================================

// Клас Program

namespace DemoOOP
{
    internal class Program
    {
        static void Main(string[] args)
        {


            Console.WriteLine("==================================");

            Console.WriteLine("Created by ctor with parameters");
            Student student2 = new Student(1234567890, "Milena", "Damesova", 4.55);
            student2.PrintData();
            Console.WriteLine(student2.CalcAvgGrade(4.55, 6.00));


        }
    }
}