C++ program to multiply three number using friend function

#include<iostream>
#include<conio.h>

class y;
class z;

class x
{
    private:
        int data;

    public:
        x()
        {
            data = 3;
        }
        friend int fun(x,y,z);
};

class y
{
    private:
        int data;

    public:
        y()
        {
            data = 2;
        }
        friend int fun(x,y,z);
};

class z
{
    private:
        int data;

    public:
        z()
        {
            data = 5;
        }
        friend int fun(x,y,z);
};

int fun(x a, y b, z c)
{
        return(a.data*b.data*c.data);
}

int main()
{
    system("cls");

    x a;
    y b;
    z c;

    std::cout<<"The result is = "<<fun(a,b,c);

    getch();
    return 0;
}

The result is = 30