Problem to deal with private access modifier

Since the variables are private than why it show no error on compiling because we call a private members  (highlighted) from another class. i know about get and set but here we use get set only for private string courseName.

 

 

using System;

public class GradeBook

{

private string courseName;

private int total;

private int gradeCounter;

private int aCount;

private int bCount;

private int cCount;

private int dCount;

public string CourseName

{

get

{

return courseName;

}

set

{

courseName = value;

}

}

public GradeBook(string name)

{

CourseName = name;

}

public void DisplayMessage()

{

Console.WriteLine("Welcome to the {0}",CourseName);

}

public void InputGrade()

{

int grade;

string input;

Console.WriteLine("{0}\n{1}","Enter the grade in the Range (0-100): ", "Type ctrl+z and press enter to terminate the input");

input=Console.ReadLine();

while(input !=null)

{

grade = Convert.ToInt32(input);

total += grade;

gradeCounter++;

IncreamentLetterGradeCounter(grade);

input = Console.ReadLine();

}

}

private void IncreamentLetterGradeCounter(int grade)

{

switch(grade/10)

{

case 9:

case 10:

aCount++;

break;

case 8:

bCount++;

break;

case 7:

cCount++;

break;

case 6:

dCount++;

break;

default:

fCount++;

break;

}//end of switch

}//end of method increament letter grade counter

public void DisplayGradeReport()

{

Console.WriteLine("Grade Report: ");

if (gradeCounter != 0)

{

double average = (double)(total / gradeCounter);

Console.WriteLine("Total of the {0} grades enter is {1}", gradeCounter, total);

Console.WriteLine("The average of class is {0:F2}", average);

Console.WriteLine("{0}A: {1}\nB: {2}\nC: {3}\nD: {4}\nF: {5}", "Number of students who recieved each grade: \n"

, aCount

, bCount

, cCount

, dCount

, fCount);

}

else

Console.WriteLine("No grades were entered");

}

}

 

 

 

 

 

 #####ANOTHER CLASS#########

using System;

class GrdaeBookTest

{

public static void Main()

{

GradeBook myBook = new GradeBook("Introduction to C#");

myBook.DisplayMessage();

myBook.InputGrade();

myBook.DisplayGradeReport();

Console.ReadLine();

}

}