《C++ Primer Plus（第六版）》（19）（第十一章 使用類 複習題答案）

1.

Test.h

#ifndef _Test_H_  
#define _Test_H_  

 
class Stonewt
{
private:
	enum {Lbs_per_stn = 14};
	int stone;
	double pds_left;
	double pounds;
public:
	Stonewt(double lbs);
	Stonewt(int stn, double lbs);
	Stonewt();
	~Stonewt();
	void show_lbs() const;
	void show_stn() const;
	operator int() const;
	operator double() const;
	Stonewt operator*(double times);
};


#endif  

Test.cpp

#include "Test.h"  
#include <iostream>  

using namespace std;
 
Stonewt::Stonewt(double lbs)
{
	stone = int(lbs) / Lbs_per_stn;
	pds_left = int(lbs) % Lbs_per_stn + lbs - int(lbs);
	pounds = lbs;
}

Stonewt::Stonewt(int stn, double lbs)
{
	stone = stn;
	pds_left = lbs;
	pounds = stn * Lbs_per_stn + lbs;
}

Stonewt::Stonewt()
{
	stone = pounds = pds_left = 0;
}

Stonewt::~Stonewt()
{

}

void Stonewt::show_lbs() const
{
	cout << pounds << " pounds\n";
}

void Stonewt::show_stn() const
{
	cout << stone << " stone, " << pds_left << " pounds\n";
}

Stonewt::operator int() const
{
	return int(pounds + 0.5);
}

Stonewt::operator double()const
{
	return pounds;
}

Stonewt Stonewt::operator*(double times)
{
	return Stonewt(pounds * times);
}

2.

成員函數是類的一部分，經過對象來調用，能夠直接訪問類成員。

友元函數不是類的一部分，直接調用，要經過成員運算符來訪問成員，不過能夠訪問私有成員。

3.

若是是私有成員，必須是友元，若是是共有的，就不要緊。

4.

Test.h

#ifndef _Test_H_  
#define _Test_H_  

 
class Stonewt
{
private:
	enum {Lbs_per_stn = 14};
	int stone;
	double pds_left;
	double pounds;
public:
	Stonewt(double lbs);
	Stonewt(int stn, double lbs);
	Stonewt();
	~Stonewt();
	void show_lbs() const;
	void show_stn() const;
	operator int() const;
	operator double() const;
	Stonewt operator*(double times);
	friend Stonewt operator*(double times, const Stonewt& a);
};


#endif  

Test.cpp

#include "Test.h"  
#include <iostream>  

using namespace std;
 
Stonewt::Stonewt(double lbs)
{
	stone = int(lbs) / Lbs_per_stn;
	pds_left = int(lbs) % Lbs_per_stn + lbs - int(lbs);
	pounds = lbs;
}

Stonewt::Stonewt(int stn, double lbs)
{
	stone = stn;
	pds_left = lbs;
	pounds = stn * Lbs_per_stn + lbs;
}

Stonewt::Stonewt()
{
	pounds = pds_left = stone = 0;
}

Stonewt::~Stonewt()
{

}

void Stonewt::show_lbs() const
{
	cout << pounds << " pounds\n";
}

void Stonewt::show_stn() const
{
	cout << stone << " stone, " << pds_left << " pounds\n";
}

Stonewt::operator int() const
{
	return int(pounds + 0.5);
}

Stonewt::operator double()const
{
	return pounds;
}

Stonewt Stonewt::operator*(double times)
{
	return Stonewt(pounds * times);
}

Stonewt operator*(double times, const Stonewt& a)
{
	return Stonewt(a.pounds * times);
}

這個東西加太多，使用int的話會有二義性。

5.

sizeof

.

::

?:

.*

6.

重載=,[],(),->必須是成員函數

7.

operator double() { return mag;}