10-Friend Function

> Friend Function is not a member function of a class to which it is a friend
> Friend function is declared in the class with friend keyword
> It must be defined outside the class to which it is friend
> Friend function can access any member of the class to which it is friend
> Friend Function can't access members of the class directly 
> It has no caller object. c1.fun();
> It should not be defined with membership label. (Complex::fun()).


> A friend function is a function that is declared outside a class, but is capable of accessing the private and protected members of class


#include <bits/stdc++.h>
using namespace std;

class Complex
{
    int a, b;

public:
    void setData(int a, int b)
    {
        (*this).a = a;
        (*this).b = b;
    }
    void showData()
    {
        printf("a = %d b = %d \n", a, b);
    }
    friend void sum(Complex);
};

void sum(Complex c)
{
    cout << "Sum is " << c.a + c.b << endl;
}

int main()
{
    Complex c1;
    c1.setData(2, 4);
    c1.showData();
    sum(c1);
}