Friend Function using C++

Friend function helps in accessing both the private and protected data of a class, by declaring it as a friend.

The function declaration should be preceded by the keyword friend. A function can be declared as a friend in any number of classes. A friend function, although not a member function, has full access rights to the private members of the class.

#include
using namespace std;
class test 
{
    private:
    int a;
    int b;
    public:
    void setvalue(){a=90;b=60;}
    friend float mean(test t);
};
float mean(test t) { return float(t.a+t.b)/2.0;}
int main()
{
    test p;
    p.setvalue();
    cout<<"Mean valu="<<mean(p)<<endl;
    
return 0;
}

A friend function can be accessed even if it is defined outside class scope. Here it is used inside the class test and then returned outside the class' scope.