C++primer plus第六版课后编程题答案11.5

#ifndef STONEWT_h_
#define STONEWT_h_
#include <iostream>
using namespace std;
enum Mode{STONE,POUNDS};//方便main115,cpp
class Stonewth
{
private:

enum {Lbs_per_stn=14};
Mode mode;
int stone;
double pds_left;
double pounds;
public:
Stonewth(double lbs)
{
mode=POUNDS;//用于控制输出什么格式
stone=int(lbs)/Lbs_per_stn;
pds_left=int(lbs)%Lbs_per_stn+lbs-int(lbs);
pounds=lbs;
};
Stonewth(){
mode=POUNDS;//默认为镑
stone=pds_left=pounds=0;
};
Stonewth(int stn,double lbs)
{
mode=POUNDS;
stone=stn;
pds_left=lbs;
pounds=stn*Lbs_per_stn+lbs;
};
void setMode(Mode form=STONE)
{
if(form==STONE)
mode=STONE;
else if(form==POUNDS)
mode=POUNDS;
else
cout<<"Invail mode !"<<endl;
}
Stonewth operator+(const Stonewth &s)const//这里我就选最简单的了
{
double newpounds=pounds+s.pounds;
return Stonewth(newpounds);
}
Stonewth operator-(const Stonewth &s)const
{
double newpounds=pounds-s.pounds;
return Stonewth(newpounds);
}
Stonewth operator*(double m)const//我这里选择重载常数*
{
double newpounds=pounds*m;
return Stonewth(newpounds);
}

friend ostream& operator<<(ostream &os,const Stonewth &s)
{
if(s.mode==STONE)
os<<s.stone<<"  stone!"<<endl;
else if(s.mode==POUNDS)
os<<s.pounds+s.pds_left<<"  pounds!"<<endl;
else
os<<"error!"<<endl;
return os;
}

};
#endif

#include <iostream>
#include "stonewt.h"
using namespace std;
void main115()
{
Stonewth s1;
Stonewth s2(10,5);
Stonewth s3(1.5);
//cout<<s2<<endl;
s2.setMode(STONE);
s3.setMode(STONE);
//cout<<s2<<endl;
//cout<<s1<<endl;
//cout<<s2<<endl;
//cout<<s3<<endl;
Stonewth s4=s2-s3;
cout<<s4<<endl;
cin.get();

}