Friend function strange behaviour - c++

Question

I'm learning C++ by myself and one of the programs that I made is sort of a school information system, it is not my first OOP program but this time I experience some strange behavior of a friend function.
I have a derived class Student which has a private member - static array of Courses objects, and finally the main container class Class which has a member - dynamic array of Students objects.
as you can see avg member of student is calculated using a friend function of Courses class (calc_avg receives an array of Courses sums it's grades and divides by course number), it works like a charm.
The problem starts once I try to calculate an average grade (class_avg) for a Class object - I use the same logic - create a friend function of Student (class_avarage that will have access to each students avg) that will receive an array of Student objects and it's size, add each students average grade and divide by array size - for some reason it receives and returns garbage values, I've been trying to fix it for 3 hours and I cant find the problem, help me if you can - here is the relevant code (independent derived classes are not included and output functions are minimized):
main //only container object creation and IO functions (all .h files included)
Class test1;
test1.input_class();
test1.output_class();
Student.h
#include "Person.h"
#include "Courses.h"
#ifndef STUDENT_H
#define STUDENT_H
class Student : public Person
{
public:
Student();
void input_student ();
void output_student ();
friend float class_avarage (Student* array, int);
~Student();
protected:
private:
Courses my_courses [6];
float avg;
};
#endif // STUDENT_H
Student.cpp
#include "Student.h"
Student::Student()
{
//ctor
}
void Student::input_student ()
{
cout << "Please enter students info:" << endl;
input_info();
my_courses[0].input_grades ("Math");
my_courses[1].input_grades ("English");
my_courses[2].input_grades ("Science");
my_courses[3].input_grades ("History");
my_courses[4].input_grades ("Art");
my_courses[5].input_grades ("Sports");
}
void Student::output_student ()
{
int i;
cout << "Students info:" << endl;
output_info();
cout << " Course Grade" << endl;
for (i = 0; i < 6; i++)
{
my_courses[i].output_grades ();
}
avg = calc_avg(my_courses, 6);
cout << " " << "Average grade for student: " << avg << endl;
}
Student::~Student()
{
//dtor
}
float calc_avg (Courses* array, int size)
{
int i;
float sum = 0;
for (i = 0; i < size; i++)
{
sum += array[i].grade;
}
return sum/size;
}
Courses.h
#include <iostream>
#include <iomanip>
#include <string>
#ifndef COURSES_H
#define COURSES_H
using std::cout;
using std::cin;
using std::endl;
using std::string;
class Courses
{
public:
Courses();
void input_grades(string);
void output_grades();
friend float calc_avg (Courses*, int);
~Courses();
protected:
private:
string course_name;
int grade;
};
#endif // COURSES_H
Courses.cpp
#include "Courses.h"
Courses::Courses() : course_name ("Default"), grade (-1)
{
//ctor
}
void Courses::input_grades (string temp_name)
{
course_name = temp_name;
cout << "Enter " << temp_name << " grade: ";
cin >> grade;
cin.get();
}
void Courses::output_grades ()
{
cout << " " << course_name << ": " << grade << endl;
}
Courses::~Courses()
{
//dtor
}
Class.h
#include <iostream>
#include <string>
#include "Teacher.h"
#include "Student.h"
#ifndef CLASS_H
#define CLASS_H
using std::cout;
using std::cin;
using std::endl;
using std::string;
class Class
{
public:
Class();
void input_class ();
void output_class ();
~Class();
protected:
private:
string class_name;
Teacher class_teacher;
Student* pupils;
int students_number;
float class_avg;
};
#endif // CLASS_H
Class.cpp
#include "Class.h"
Class::Class() : class_name ("A"), pupils (NULL), students_number (0), class_avg (0)
{
//ctor
}
void Class::input_class ()
{
int i;
//input class data
cin >> students_number;
cin.get();
pupils = new (std::nothrow) Student [students_number];
if (!pupils)
{
cout << "Allocation failed!" << endl;
}
else
{
for (i = 0; i < students_number; i++)
{
pupils[i].input_student();
}
}
class_avg = class_avarage (pupils, students_number);
}
void Class::output_class ()
{
int i;
cout << " Displaying info of class :" << class_name << endl <<
" Class average grade: " << class_avg << endl;
class_teacher.output_teacher();
cout << " Number of students: " << students_number << endl << " Students: " << endl;
for (i = 0; i < students_number; i++)
{
pupils[i].output_student();
}
}
Class::~Class()
{
//dtor
}
float class_avarage (Student* array, int size)
{
cout << size << endl;
int i;
float total = 0;
for (i = 0; i < size; i++)
{
total += array[i].avg;
}
return total/size;
}

Answer 1

Why should anyone want to use friend functions? Just add simple getter for Cource.grade member and lasy getter for Student.avg. This will eliminate the possibility to get garbage instead of data.
Also, use std::vector and pass them throught std::vector&, not arrays and pointers.