怎么补齐啊，不知道怎么加

#include
using namespace std;
class A
{
public:
A(){cout<<"AA"; }
~A(){cout<<"DA"; }
};
class B
{
A a;
public:
B(){cout<<"BB"; }
~B(){cout<<"DB"; }
};
int main()
{
B b;
cout<<"CC";
return 0;
}

哪里要补？

没缺什么，要补啥
主要是构造函数和析构函数的运行顺序：

#include<iostream>
using namespace std;
class A
{
public:
    A(){cout<<"AA"; }
    ~A(){cout<<"DA"; }
};
class B
{
    A a;
public:
    B(){cout<<"BB"; }
    ~B(){cout<<"DB"; }
};
int main()
{
    B b;
    cout<<"CC";
    return 0;
}