C++——类静态成员和友元函数 – 作者:Johnson666

编程题

1.静态成员的使用

代码：

#include<iostream>
using namespace std;
class Time
{
public:
	static int totalTime;
	Time(int a,int b,int c);
	void ShowTime()
{
	cout<<"hour:"<<hour<<" minute:"<<minute<<" second:"<<second<<endl;
}
	static void ShowTotalTime();
	~Time(){}
private:
	int hour;
	int minute;
	int second;
	
};
void Time::ShowTotalTime()
{cout<<"totalTime:"<<Time::totalTime<<endl;}
int Time::totalTime=0;
Time::Time(int h,int m,int s):hour(h),minute(m),second(s)
	{
	
	totalTime=hour*60*60+minute*60+second;
	}
int main ()
{
Time a(1,20,30);
a.ShowTime();
a.ShowTotalTime();
cout<<"totalTime:"<<a.totalTime<<endl;
Time::ShowTotalTime();
cout<<"totalTime:"<<Time::totalTime<<endl;
return  0;
}

结果：

2.友元函数的使用

代码：

#include<iostream>
using namespace std;
class Rectangle
{
public:
Rectangle(int l,int h,int w)
{
length=l; height=h;width=w;
}
void Show();
void SetValue(int a,int b,int c);
friend void Area(Rectangle R);
~Rectangle(){}
private:
int length;
int height;
int width;
};
void Rectangle::Show()
{
	cout<<"length:"<<length<<" height:"<<height<<" width:"<<width<<endl;
}
void Rectangle::SetValue(int a,int b,int c)
{
length=a;height=b;width=c;
}
 void Area(Rectangle R)
{
	cout<<"Area:"<<R.length*R.height*R.width<<endl;

}
int main ()
{
Rectangle R(5,10,15);
R.Show();
Area(R);
R.SetValue(20,15,5);
R.Show();
Area(R);
return  0;
}

结果：

3.类中静态成员的使用方法

代码：

#include<iostream>
using namespace std;
class A
{
public:
	A(int i)
	{
		a = i;
	}
	int geta()
	{
		return a;
	}
	static int getb()
	{
		return b;
	}
	static void setb()
	{
		b = b + 1;
	}
private:
	int a;
	static int b;
};
int A::b = 10;
int main()
{
	A a1(1),a2(2);
	cout << a1.geta() << "," << a1.getb() << endl;
	cout << a2.geta() << "," << a2.getb() << endl;
	a1.setb();
	A::setb();
	cout << a1.geta() << "," << a1.getb() << endl;
	cout << a2.geta() << "," << a2.getb() << endl;
	return 0;
}

结果：

4.友元函数的使用方法

代码：

#include<iostream>
using namespace std;
class Internet
{
public:
	Internet(char *name,char *address)
	{
		strcpy(Internet::name,name);
		strcpy(Internet::address,address);
	}
	friend void ShowN(Internet &obj);
private:
	char name[20];
	char address[20];
};
void ShowN(Internet &obj)
{
	cout << obj.name << "," << obj.address << endl;
}
int main()
{
	Internet a("新浪","www.sina.com.cn");
	ShowN(a);
	return 0;
}

结果：

5.定义一个Cat类，用静态成员变量num记录Cat的个体数目，用静态成员函数getNum读取num的值。设计程序测试这个类，体会静态成员变量和静态成员函数的用法。

代码：

#include<iostream>
using namespace std;
class Cat
{
public:
	void get(int m)
	{
		numOfCats += m;
	}
	static int getNumOfCats()
	{
		cout << numOfCats << endl;
		return 0;
	}
private:
	static int numOfCats;
};
int Cat::numOfCats = 1;
int main()
{
	Cat c;
	cout << "Num:";
	Cat::getNumOfCats();
	c.get(4);
	cout << "Num:";
	Cat::getNumOfCats();
	return 0;
} 

结果：

6.定义Boat和Car两个类，二者都有weight属性，定义二者的一个友元函数getTotalWeight，计算二者的重量和。

代码：

#include <iostream>
using namespace std;
class Boat
{
public:
friend int getTotalWeight(Boat b);
int weight;
Boat(int a)
{weight=a;}
};
class Car
{
public:
	int weight;
	Car(int c)
	{weight=c;}
	int getTotalWeight(Boat b);
};
int Car::getTotalWeight(Boat b)
{
int T;
T=b.weight+weight;
return T;
}
int main ()
{
int TT; 
Boat b(100);
Car c(150);
TT=c.getTotalWeight(b);
cout<<"Boat和Car的重量和为:"<<TT<<"公斤"<<endl;
return  0; 
}

结果：

7.已知Time类（包含私有成员变量hour，minute，sec），Date类（包含私有成员变量month，day，year），两者都由成员函数display进行成员变量的输出，要求将Time类声明为Date类的友元类，通过Time类的display函数引用Date类对象的私有数据，输出年、月、日和时、分、秒。

代码：

#include <iostream>
using namespace std;
class Date
{
public:
friend class Time;
Date()
{
year=2021;
month=5;
day=11;
}
void display()
{
	cout<<"日期为:"<<year<<"/"<<month<<"/"<<day<<endl;
}
private:
int year;
int month;
int day;	
};
class Time
{
public:
Time(int a,int b,int c)
{
hour=a;
minute=b;
sec=c;
}
void display()
{
d.display();
cout<<"时间为:"<<hour<<":"<<minute<<":"<<sec<<endl;
cout<<"当前日期时间为:"<<d.year<<"/"<<d.month<<"/"<<d.day<<"  "<<hour<<":"<<minute<<":"<<sec<<endl;
}
private:
Date d;
int hour;
int minute;
int sec;
};
int main ()
{
Time t(20,30,10);
t.display();
return  0; 
}

结果：

来源：freebuf.com 2021-05-15 22:56:19 by: Johnson666