Adding arrays from different classes using friend function [cpp]

Q:write a CPP program to declare 3 classes perform the addition of the data members in first 2 classes and result in the 3rd class using friend function

DEFINITION:
friend function:In object-oriented programming, a friend function that is a "friend" of a given class is allowed access to private and protected data in that class that it would not normally be able to as if the data was public . Normally, a function that is defined outside of a class cannot access such information.

PROGRAM:

#include <iostream>
#include<conio.h>
using namespace std;
void add();
class A{
    int a[10],limit;
public:
    A(int m){
        limit=m;
        cout<<"enter array"<<endl;
        for(int i=0;i<limit;i++)
        cin>>a[i];
    }
    friend void add();


};

class B{
    int a[10],limit;
public:
    B(int m){
        limit=m;
        cout<<"enter array"<<endl;
        for(int i=0;i<limit;i++)
        cin>>a[i];
    }
    friend void add();


};

class C{
    int a[10],limit;
public:
    C(){
        limit=0;
        }
    friend void add();

    void addToC(int k){
    a[limit]=k;
    limit++;
    }
    void showC(){
    for(int i=0;i<limit;i++)
        cout<<a[i]<<" ";
    }
};

int main()
{

    add();
}

void add(){
    int limit;
    cout<<"limit:";
    cin>>limit;
    A a(limit);
    B b(limit);
    C c;
    for(int i=0;i<limit;i++)
            c.addToC(a.a[i]+b.a[i]);
    c.showC();

}