3.9 static练习和强化练习

计算长方体的体积

#include
using namespace std;

class Box
{
public:
    Box(int l,int w)
    {
        len = l;
        width = w;
    }

    int volume()
    {
        int v = len*width*hight;
        cout << "高度是" << hight << endl;
        cout << "体积是" << v << endl;
        return v;
    }

    static void changeHight(int h)
    {
        hight = h;
    }

private:
    static int hight;
    int len;
    int width;
};

int Box::hight = 100;

int main()
{

    Box b1(10,20);
    Box b2(100,200);
    b1.volume();
    b2.volume();

    Box::changeHight(300);
    b1.volume();
    b2.volume();//说明静态是整个类共享的
    return 0;
}

学生的成绩问题

#include
using namespace std;

class Student
{
public:
    Student(int id,double score)
    {
        //创建一个学生
        m_id = id;
        m_score = score;

        m_count++;//累加学生个数
        sum_score += score; //加后赋值运算符，sum_score = sum_score + score
                            //但前者效率高些
    }

    static int getCount()
    {
        return m_count;
    }

    static double getAvg()
    { 
        return sum_score/m_count;
    }

    ~Student() {
        m_count --;
        sum_score -= m_count;
    }
private:
    int m_id;
    double m_score;//得分

    //统计学生个数的静态成员变量
    static int m_count;

    //统计学生总分数的静态成员变量
    static double sum_score;
};
//初始化静态变量
int Student::m_count = 0;
double Student::sum_score = 0;

int main()
{
    Student s1(1,80);
    Student s2(2,90);
    Student s3(3,100);

    cout << "学生总人数" << Student::getCount() << endl;
    cout << "学生的平均分" << Student::getAvg() << endl;

    return 0;
}

——————————————————————

#include
using namespace std;

class Goods
{
public:
    Goods()
    {
        //没什么实际意义
        weight = 0;
        next = NULL;
        cout << "创建了一个重量为" << weight << "的货物" << endl;
    }

    Goods(int w)
    {
        //需要创建一个w的货物，并且仓库加上这个重量
        weight = w;
        next = NULL;
        total_weight += w;
        cout << "创建了一个重量为" << weight << "的货物" << endl;
    }

    ~Goods() {
        //仓库减少这个货物的重量
        cout << "删除了一箱重量是" << weight << "的货物" << endl;
        total_weight -= weight;
    }

    static int get_total_weight()
    {
        return total_weight;
    }

    Goods *next;
private:
    int weight;//重量
    static int total_weight;//仓库总重量
};

int Goods::total_weight = 0;

void buy(Goods * &head,int w)//改变一级指针用二级指针 或一级+引用
{
    //创建一个货物 ，重量是w
    Goods  *new_goods = new Goods(w);

    //使用链表，从头部插入链表，画图清楚些（找工作笔试前要看链表）
    if (head == NULL) {
        head = new_goods;
    }
    else {
        new_goods->next = head;
        head = new_goods;
    }
}

void sale(Goods * &head)
{
    if (head == NULL)
    {
        cout << "仓库中已经没有货物了" << endl;   
        return ;
    }
    //删头
    Goods *temp = head;
    head = head->next;

    delete temp;
    cout << "saled." << endl;   
}

int main()
{
    int choice = 0;
    Goods *head =NULL;//头指针
    int w;
    do {
         cout << "1 进货" << endl;
         cout << "2 出货" << endl;
         cout << "3 退出" << endl;
         cin >> choice;
         switch (choice)
         {
             case 1:
                 //进货
                 cout << "请输入要创建的重量" << endl;
                 cin >> w;
                 buy(head,w);
                 break;
             case 2:
                //出货
                sale(head);
                break;
            case 0:
                //退出
                return 0;
            default:
            break;
         }  
         cout << "当前仓库的总重量是" << Goods::get_total_weight() << endl;
    }while(1);

    return 0;
}

总结 ：

sum_score += score;

+=：加后赋值运算符，sum_score = sum_score + score
但前者效率高些**

强化练习中使用了链表，从头部插入链表，删除从头部删，画图会清楚些（找工作笔试经常会考链表，建议笔试前看看）