C++重点和练习

 作业题目：

#include <iostream>
using namespace std;
class Rec
{
   const int length;
   int width;
public:
   void set_length(int l);
   void set_width(int w);
   int get_length();
   int get_width();
   void show();
};

#include <iostream>
using namespace std;
class Cir
{
    int &r;
public:
    void set_r(int r);  //设置私有属性r的值
    void show(double PI=3.14);   //参数有默认值3.14
};

#include <iostream>
using namespace std;
class Car  //类名首字母一般大小
{
    string color;
    string brand;
    int speed;
public:
    void set(string c,string b,int s);
    void display();
    void acc(int a);
};

答案：

#include <iostream>

using namespace std;

class Rectangle
{
    const int length;
    int width;
public:
//    void set_length(int len);
    Rectangle(int length):length(length){}
    void set_width(int wid);
    int get_length();
    int get_width();
    void show();
};

//Rectangle R3;
//void Rectangle::set_length(int len)
//{
//   length = len;
//}

void Rectangle::set_width(int width)
{
   this->width = width;
}

int Rectangle::get_length()
{
    return length;
}
int Rectangle::get_width()
{
    return width;
}
void Rectangle::show()
{
    cout << this << endl;
    int s = 2*(width+length);
    int area = width*length;
    cout << "周长：" << s << "\t"
         << "面积：" << area << endl;
}

class Circle
{
    int &r;
public:
    Circle(int &r1):r(r1){}
    void set_r(int tr);
    void show(float PI = 3.14);
};

void Circle::set_r(int tr)
{
    r = tr;
}
void Circle::show(float PI)
{
    float s = PI*2*r;
    float area = PI*r*r;
    cout << "周长：" << s << "\t"
         << "面积：" << area << endl;
}

class Car
{
    string color;
    string brand;
    float speed;
public:
    Car():color("red"),brand("玛莎拉蒂"),speed(360){}
    void display();
    void acc(int a);
    void set_color(string c);
    void set_brand(string b);
    void set_speed(float s);


};

void Car::display()
{
    cout << "颜色：" << color << "\t"
         << "品牌：" << brand << "\t"
         << "速度：" << speed
         << endl;
}
void Car::set_color(string c)
{
    color = c;
}
void Car::set_brand(string b)
{
    brand = b;
}
void Car::set_speed(float s)
{
    speed = s;
}
void Car::acc(int a)
{
    speed += a;
}



int main()
{
    Rectangle rec1(3);
    rec1.set_width(3);
    cout << "rec1长度：" << rec1.get_length() << "\t"
         << "rec1宽度：" << rec1.get_width()  <<endl;
    rec1.show();

    int r = 1;
    Circle r1(r);
    r1.show();
    r1.set_r(2);
    r1.show();

    Car car1;
    car1.display();
    car1.set_color("red");
    car1.set_brand("奥迪");
    car1.set_speed(240);
    car1.display();
    car1.acc(5);
    car1.display();

    return 0;
}

自己定义构造函数：

#include <iostream>
#include <cstdlib>
using namespace std;
class Stu
{
    int age;
    double score;
public:
    //Stu(){cout << "Stu的无参构造" << endl;}
    //实现Stu的有参构造
    Stu(int age,double score)
    {
        this->age = age;
        this->score = score;
        cout << "Stu的有参构造" << endl;
    }
    void show();
};
void Stu::show()
{
    cout << "age = " << age << endl;
    cout << "score = " << score << endl;
}
int main()
{
    //Stu s1;
    //Stu *p1 = (Stu*)malloc(sizeof(Stu));
    Stu *p1;
    cout << "*********" << endl;
    p1 = new Stu(1,3.14);  // new Stu{1,3.14}也可以  
    //类中只提供了有参构造，所以new申请空间时必须给初始值可以用{},也可以用()
    p1->show();
    //Stu s1(12,31.9);   //调用了有参构造
    return 0;
}

参数和成员属性同名：

#include <iostream>
#include <cstdlib>
using namespace std;
class Stu
{
    int age;
    double score;
public:
    Stu(int age,double score):age(age),score(score)
    {cout << "Stu有两个参数的有参构造" << endl;}
    void show();
};
void Stu::show()
{
    cout << "age = " << age << endl;
    cout << "score = " << score << endl;
}
int main()
{
    Stu s2(12,31.9);
    s2.show();
    return 0;
}

类中存在引用成员时：
 

#include <iostream>
#include <cstdlib>
using namespace std;
class Stu
{
    int &age;
    double score;
public:
    Stu(int &age,double score):age(age),score(score)
    {cout << "Stu有两个参数的有参构造" << endl;}
    void show();
    void set_age()
    {age=0;}
};
void Stu::show()
{
    cout << "age = " << age << endl;
    cout << "score = " << score << endl;
}
int main()
{
    int age = 18;
    Stu s2(age,31.9);
    s2.show();
    s2.set_age();
    cout << age << endl;  //局部变量age的值为0，因为类对象中的age引用了该局部变量
    return 0;
}

类中存在const修饰的成员时：
 

#include <iostream>
#include <cstdlib>
using namespace std;
class Stu
{
    const int age;
    double score;
public:
    //Stu():age(23){cout << "Stu的无参构造" << endl;}
    //实现Stu的有参构造
    Stu(int age,double score):age(age),score(score)
    {cout << "Stu有两个参数的有参构造" << endl;}
    Stu(int age):age(age)
    {cout << "Stu有一个参数age的有参构造" << endl;}
    /*Stu(double score):age(20)
    {
        this->score = score;
        cout << "Stu有一个参数score的有参构造" << endl;
    }*/
    void show();
};
void Stu::show()
{
    cout << "age = " << age << endl;
    cout << "score = " << score << endl;
}
int main()
{
    int age = 18;
    Stu s2(age,31.9);
    s2.show();
    Stu s1(24);
    s1.show();
    return 0;
}

类中存在其他类对象时：

#include <iostream>
using namespace std;
class Stu
{
    int age;
    float score;
public:
    Stu(int age,float score):age(age),score(score){}
    int get_age()
    {
        return age;
    }
    double get_score()
    {
        return score;
    }
};
class Person
{
    const int id;
    const string name;
    Stu stu1;
public:
    Person(int id,string name,Stu stu1):id(id),name(name),stu1(stu1){}
    Person(int id,string name,int age,float score):id(id),name(name),stu1(age,score){}
    void show()
    {
        cout << "id = " << id << "\t"
             << "name = " << name << "\t"
             << "age = " << stu1.get_age() << "\t"
             << "score = " << stu1.get_score() << endl;
    }
};

int main()
{
    Stu stu1(18,99.9);
    Person p1(10086,"张三",stu1);
    p1.show();
    Person p2(10085,"李四",19,88.8);
    p2.show();
    return 0;
}