第三周:程序设计预算法(三)

题面

001:返回什么才好呢

未懂

1.A& GetObj()//没有明白此处的this指针,定义这个函数的作用为没有明白

#include <iostream>
using namespace std;
class A {
public:
    int val;

    A(int
// 在此处补充你的代码
 n=123)
    {
        val = n;
    }
    A& GetObj()//没有明白此处的this指针,定义这个函数的作用为没有明白
    {
        return *this;
    }
};
int main()
{
    int m,n;
    A a;
    cout << a.val << endl;
    while(cin >> m >> n) {
        a.GetObj() = m;
        cout << a.val << endl;
        a.GetObj() = A(n);
        cout << a.val<< endl;
    }
    return 0;
}

002:Big & Base 封闭类问题

#include <iostream>
#include <string>
using namespace std;
class Base {
public:
    int k;
    Base(int n):k(n) { }
};
class Big
{
public:
    int v;
    Base b;
// 在此处补充你的代码
Big(int n):v(n),b(n){}//忘记叫啥链表了,反正是赋值用的！
};
int main()
{
    int n;
    while(cin >>n) {
        Big a1(n);
        Big a2 = a1;
        cout << a1.v << "," << a1.b.k << endl;
        cout << a2.v << "," << a2.b.k << endl;
    }
}

003:编程填空：统计动物数量（不会标记）

恕我直言整道题我都不懂

#include <iostream>
using namespace std;
// 在此处补充你的代码
class Animal{
public:
    static int number;
    Animal(){
        number++;
    }
    virtual ~Animal()
    {
        number--;
    }
};
int Animal::number=0;
class Dog:public Animal{
public:
    static int number;
    Dog()
    {
        number++;
    }
    ~Dog()
    {
        number--;
    }
};
int Dog::number=0;
class Cat :public Animal{
public:
    static int number;
    Cat()
    {
        number++;
    }
    ~Cat()
    {
        number--;
    }
};
int Cat::number=0;
void print() {
    cout << Animal::number << " animals in the zoo, " << Dog::number << " of them are dogs, " << Cat::number << " of them are cats" << endl;
}
void print() {
    cout << Animal::number << " animals in the zoo, " << Dog::number << " of them are dogs, " << Cat::number << " of them are cats" << endl;
}

int main() {
    print();
    Dog d1, d2;
    Cat c1;
    print();
    Dog* d3 = new Dog();
    Animal* c2 = new Cat;
    Cat* c3 = new Cat;
    print();
    delete c3;
    delete c2;
    delete d3;
    print();
}

004:这个指针哪来的

要学常变量对象的定义形式

#include <iostream>
using namespace std;

struct A
{
    int v;
    A(int vv):v(vv) { }
// 在此处补充你的代码
    const A* getPointer() const//如果定义的不是指针的返回的只是地址不是值
    {
        return this;
    }
};

int main()
{
    const A a(10);
    const A * p = a.getPointer();//常变量只能调用常变量函数,故定义的函数也必须是常变量函数
    cout << p->v << endl;
    return 0;
}