27friendclass.cpp

#include <iostream>
using namespace std;

// forward declaration : it is necessary to garauntee that a class is going to exist
class complex;

class calculator // the class that will take the data of other class is declared earlier
{
public:
    int add(int a, int b)
    {
        return (a + b);
    }
    int sumReaLcomplex(complex, complex); // here the arguments should be provided when function is defined
    int sumImaGcomplex(complex, complex);
};

class complex
{
    int a, b;

    // Individually declaring each function of a class as friend

    friend int calculator ::sumReaLcomplex(complex, complex);
    friend int calculator ::sumImaGcomplex(complex, complex);

    /*Here, the friend function is declared which is a part of another class
    the argument variables or names aren't provided as they have no garauntee unless the function is defined*/

    // declaring the entire calculator class as a friend to give all functions of it access to complex's private data
    friend class calculator;

public:
    void setnum(int n1, int n2)
    {
        a = n1;
        b = n2;
    }
    void printnum()
    {
        cout << "z = " << a << " + " << b << "i" << endl;
    }
};
int calculator ::sumReaLcomplex(complex o1, complex o2) // declaration of a class function
{
    return (o1.a + o2.a);
}
int calculator ::sumImaGcomplex(complex o1, complex o2) // declaration of a class function
{
    return (o1.b + o2.b);
}

int main()
{
    complex c1, c2;
    c1.setnum(1, 6);
    c1.printnum();

    c2.setnum(7, 3);
    c2.printnum();

    calculator calculationR, calculationI;
    int sumr = calculationR.sumReaLcomplex(c1, c2);
    // here the access is done since it is function in a class scope, it only required to access data of other class
    cout << "Real part of z1 + z2 is r = " << sumr << endl;

    // Another friend function
    int sumi = calculationI.sumImaGcomplex(c1, c2);
    cout << "Imaginery part of z1 + z2 is i = " << sumi << endl;
    return 0;
}