using System;

public class Student {

    //properties

    public string name { get; set; }

    public int age { get; set; }

    private double _gpa;

    public double gpa{

        get{ return _gpa; }

        set{

            if(value >= 0){

                _gpa = value;

            } else {

                Console.WriteLine("GPA not changed: GPA must be entered as a non-negative number");

            }

        }

    }

    //constructors

    public Student(){}

    public Student(string iName, int iAge, double iGpa){

        name = iName;

        age = iAge;

        gpa = iGpa;

    }

    //functions

    public double show_gpa(string adj){

        if(adj == "adjusted"){

            return gpa * 1.15;

        }

        return gpa;

    }

    public bool lucky_draw(){

        if(age % 4 == 0){

            return true;

        }

        return false;

    }

}

​

public class Program {

    public static void CallFunction(int iInput, ref double dInput){

        iInput = iInput + 1;

        dInput = dInput + 1;

    }

    public static void Main(){

        string strName = "Mary";

        int iAge = 18;

        double dGPA = 3.6;

        Student me = new Student(strName, iAge, dGPA);

        Console.WriteLine(me.show_gpa("regular"));

        Console.WriteLine(me.show_gpa("adjusted"));

        Console.WriteLine(me.lucky_draw());

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

        Console.WriteLine("Age:{0}, GPA:{1}",iAge, dGPA);

        //output: Age:18, GPA:3.6

        CallFunction(iAge, ref dGPA);

        Console.WriteLine("Age:{0}, GPA:{1}",iAge, dGPA);

        //output: Age:18, GPA:4.6

        /*

        calling by reference allows a method to change the value of an initialized variable that the method is passing; dGPA changed because dGPA is being passed with

        the ref keyword as the dInput parameter while iAge is being passed with no ref keyword as the iInput parameter: Setting dInput equal to something else will also

        change the value of dGPA outside the CallFunction method since they are being treated as the same variable.

        */

    }

}