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课上类的三个练习题的构造函数
1.
 

#include <iostream>
using namespace std;
class Rec
{int length;int width;
public:Rec(int length,int width):length(length),width(width){}void set_length(int l);void set_width(int w);int get_length();int get_width();void show();
};
//类外定义成员方法
void Rec::set_length(int l)
{length = l;
}
void Rec::set_width(int w)
{width = w;
}
int Rec::get_length()
{return length;   //将长度的值返回给调用处
}
int Rec::get_width()
{return width;
}
void Rec::show()
{cout << "周长为:" << 2*(length+width) << endl;cout << "面积是:" << length*width << endl;
}
int main()
{//实例化类对象Rec r1(4,5);r1.set_length(2);r1.set_width(3);int a = r1.get_width();cout << a << endl;r1.show();return 0;
}

2.

#include <iostream>
using namespace std;
class Cir
{int r;
public:Cir(int &r):r(r){}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
};
void Cir::set_r(int r1)
{r = r1;
}
void Cir::show(double PI)
{cout << "周长:" << 2*r*PI << endl;cout << "面积:" << r*r*PI << endl;
}
int main()
{int r =1;Cir c1(r);c1.show();c1.set_r(4);c1.show();return 0;
}

3.

#include <iostream>using namespace std;//定义了一个Stu类
class Car
{string color;string brand;int speed;
public://为类中的私有成员获取值Car(string color,string brand,int speed):color(color),brand(brand),speed(speed){}void display();//公有的成员函数void acc(int a);void set(string p,string color,int s);
};
void Car::set(string p,string c,int s)
{brand = p;color = c;speed = s;}
void Car::acc(int s1)
{speed += s1;
}
void Car::display()
{cout<< "品牌："<<brand;cout<< "颜色："<<color;cout<< "速度："<<speed<<"km/h";
}
int main()
{Car s1("紫色","小米",99);s1.display();cout<<endl;s1.set("奥迪","黑色",100);s1.display();s1.acc(10);s1.display();return 0;
}