C++填空题--多态与虚函数

下列程序中声明两个类First和Second ，其中函数“print”是类 First类的成员函数，是类Second的友元函数。请将程序补充完整，使程序输出结果为：First:6 Second:8

#include <iostream>
using namespace std;
_____________
class First
{
private:
    int t;
public:
    First(int x) { t = x; }
    void print(Second &b);
};
class Second
{
private:
    int s;
public:
    Second(int y) { s = y; }
    friend void  ________print(Second &w);
};
______________
{
    cout << "First: " << t << " Second: " << w.s << endl;
}
int main()
{
    First m(6);
    Second n(8);
    m.print(n);
    return 0;
}

从上到下3个空分别是：
class Second;
First::
void First::print(Second &w)

程序输出为：
First: 6 Second: 8

参考如下：

#include <iostream>
using namespace std;

class Second;
class First
{
private:
    int t;
public:
    First(int x) { t = x; }
    void print(Second &b);
};
class Second
{
private:
    int s;
public:
    Second(int y) { s = y; }
    friend void First::print(Second &w);
};
void First::print(Second &w)
{
    cout << "First: " << t << " Second: " << w.s << endl;
}
int main()
{
    First m(6);
    Second n(8);
    m.print(n);
    return 0;
}