菜鸟的提问：关于C++类的组合的疑问，我这串代码哪儿错了

Question

#include
using namespace std;
class CPU
{
CPU(int c=1);
};
class RAM
{
RAM(int ram=2);
};
class CDROM
{
CDROM(int cdrom=3);
};
class Computer
{
public:
Computer(CPU c,RAM r,CDROM d);
~Computer();
void run()
{
cout<<"cpu为:"<<cpu<<" "<<"ram为:"<<ram<<" "<<"cdrom为:"<<cdrom<<endl;
cout<<"调用的是这个run函数"<<endl;
}
void stop()
{
cout<<"调用的是这个stop函数"<<endl;
}
private:
CPU cpu;
RAM ram;
CDROM cdrom;
};
Computer::Computer(CPU c,RAM r,CDROM d):cpu(c),ram(r),cdrom(d)
{
cout<<"调用的是构造函数"<<endl;
}
Computer::~Computer()
{
cout<<"调用的是该析构函数"<<endl;
}
int main()
{
Computer thing();
thing.run();
thing.stop();
return 0;
}

Answer 1

#include <iostream>

using namespace std;

class CPU
{
private:
    int val;
public:
    CPU(int c = 1) { val = c; }
    friend ostream& operator << (ostream& output, CPU& c)
    {
        output << "CPU" << c.val;
        return output;
    }
};
class RAM
{
private:
    int val;
public:
    RAM(int ram = 2) { val = ram; }
    friend ostream& operator << (ostream& output, RAM& r)
    {
        output << "RAM" << r.val;
        return output;
    }
};
class CDROM
{
private:
    int val;
public:
    CDROM(int cdrom = 3) { val = cdrom; }
    friend ostream& operator << (ostream& output, CDROM& c)
    {
        output << "CDROM" << c.val;
        return output;
    }
};
class Computer
{
public:
    Computer(CPU c, RAM r, CDROM d);
    ~Computer();
    void run()
    {
        cout << "cpu为:" << cpu << " " << "ram为:" << ram << " " << "cdrom为:" << cdrom << endl;
        cout << "调用的是这个run函数" << endl;
    }
    void stop()
    {
        cout << "调用的是这个stop函数" << endl;
    }
private:
    CPU cpu;
    RAM ram;
    CDROM cdrom;
};
Computer::Computer(CPU c, RAM r, CDROM d) :cpu(c), ram(r), cdrom(d)
{
    cout << "调用的是构造函数" << endl;
}
Computer::~Computer()
{
    cout << "调用的是该析构函数" << endl;
}
int main()
{
    CPU c;
    RAM r;
    CDROM cd;
    Computer thing(c, r, cd);
    thing.run();
    thing.stop();
    return 0;
}