mooc程序设计与算法（三）C++面向对象程序设计 类和对象提高 编程作业

1:返回什么才好呢
答案：

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

    A(int
i){
        //有参构造函数
        val=i;
    }

    A(){
        //无参构造函数
        val=123;
    }

    A& GetObj(){
        return *this; //这里返回this指针，就是，把这个对象返回回去了
    }
};
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;
}

2、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;
Big(int _n):b(_n), v(_n){}
};
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;
    }
}

3、编程填空：统计动物数量

#include <iostream>
using namespace std;
class Animal{
public:
    static int number;
    Animal(){

    }
    virtual ~Animal(){//这里用虚析够函数，为了让继承它的两个子类的析够函数起作用
    }
};
int Animal::number = 0;

class Dog:public Animal{
public:
    static int number;
    Dog(){
        Animal::number++;
        number++;
    }
    ~Dog(){
        Animal::number--;
        number--;
    }
};
int Dog::number = 0;
class Cat:public Animal{
public:
    static int number;
    Cat(){
        Animal::number++;
        number++;
    }
    ~Cat(){
        Animal::number--;
        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;
}

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();
}

4、这个指针哪来的

#include <iostream>
using namespace std;

struct A
{
    int v;
    A(int vv):v(vv) { }
const A* getPointer() const {
        return this;
    }
};

int main()
{
    const A a(10);
    const A * p = a.getPointer();
    cout << p->v << endl;
    return 0;
}