am confused with this please help me

#include<iostream>
using namespace std;

class AClass {
private:
int a,b;
public:
void test() {
a=10;
b=20;
}
// Declare the two functions friends.
friend int add(AClass input);
friend int minus(AClass input);
};

// Function one
int add(AClass input) {
return int(input.a + input.b);
}

// Function two
int minus(AClass input) {
return int(input.b – input.a);
}

void main(void){
AClass output;
// Initialize output
output.test();
cout << add(output) << endl;
cout << minus(output) << endl;
}

I hope this answers your question.

A friend function is used for accessing the non-public members of a class. A class can allow non-member functions and other classes to access its own private data, by making them friends. Thus, a friend function is an ordinary function or a member of another class. A friend class has full access of private data members of another class without being member of that class.