程序清单11.7，11.8，11.9——课本316，317，318页，重载减，乘运算符

mytime2.h

#ifndef MTTIME2_H
#define MYTIME2_H

class Time
{
private:
int hours;
int minutes;
public:
Time();
Time(int h,int m=0);
void AddMin(int m);
void AddHr(int h);
void Reset(int h=0,int m=0);
Time operator+(const Time & t) const;
Time operator-(const Time & t) const;
Time operator*(double n) const;
void Show() const;
};
#endif

mytime2.cpp

#include<iostream>
#include"mytime2.h"

using namespace std;
Time::Time()
{
hours=minutes=0;
}

Time::Time(int h,int m)
{
hours=h;
minutes=m;
}

void Time::AddMin(int m)
{
minutes+=m;
hours+=minutes/60;
minutes%=60;
}

void Time::AddHr(int h)
{
hours+=h;
}

void Time::Reset(int h,int m)
{
hours=h;
minutes=m;
}

Time Time::operator+(const Time & t) const
{
Time sum;
sum.minutes=minutes+t.minutes;
sum.hours=hours+t.hours+sum.minutes/60;
sum.minutes%=60;
return sum;
}

Time Time::operator-(const Time & t) const
{
Time diff;
int tot1,tot2;
tot1=t.minutes+60*t.hours;
tot2=minutes+60*hours;
diff.minutes=(tot2-tot1)%60;
diff.hours=(tot2-tot1)/60;
return diff;
}

Time Time::operator*(double mult) const
{
Time result;
long totalminutes=hours*mult*60+minutes*mult;
result.hours=totalminutes/60;
result.minutes=totalminutes%60;
return result;
}

void Time::Show() const
{
cout<<hours<<" hours，"<<minutes<<" minutes";
}

usetime.cpp

#include<iostream>
#include"mytime2.h"
using namespace std;

int main()
{
Time weeding(4,35);
Time waxing(2,47);
Time total;
Time diff;
Time adjusted;

cout<<"Waxing time = ";
waxing.Show();
cout<<endl;

cout<<"total word time = ";
total=weeding+waxing;
total.Show();
cout<<endl;

diff=weeding-waxing;
cout<<"weeding time - waxing time = ";
diff.Show();
cout<<endl;

adjusted=total*1.5;
cout<<"adjusted work time = ";
adjusted.Show();
cout<<endl;

system("pause");
return 0;
}