C++ Primer Plus第六版编程练习11.4解答

mytime3.h

// mytime3.h -- Time class with friends
#ifndef MYTIME3_H_
#define MYTIME3_H_
#include <iostream>

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);
friend Time operator+(const Time & t1, const Time & t2);
friend Time operator-(const Time & t1, const Time & t2);
friend Time operator*(const Time & t, double mult);
friend Time operator*(double mult, const Time & t)
{ return t * mult; } // inline definition
friend std::ostream & operator<<(std::ostream & os, const Time & t);

};
#endif


mytime3.cpp
// mytime3.cpp -- implementing Time methods
#include "mytime3.h"

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 operator+(const Time & t1, const Time & t2)
//注意这里不要用Time::限定符，因为友元函数不是类的成员函数！
{
Time sum;
sum.minutes = t1.minutes + t2.minutes;
sum.hours = t1.hours + t2.hours + sum.minutes / 60;
sum.minutes %= 60;
return sum;
}

Time operator-(const Time & t1, const Time & t2)
{
Time diff;
int tot1, tot2;
tot1 = t1.minutes + 60 * t1.hours;
tot2 = t2.minutes + 60 * t2.hours;
diff.minutes = (tot2 - tot1) % 60;
diff.hours = (tot2 - tot1) / 60;
return diff;
}

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

std::ostream & operator<<(std::ostream & os, const Time & t)
{
os << t.hours << " hours, " << t.minutes << " minutes";
return os;
}


usemytime3.cpp
//usetime3.cpp -- using the fourth draft of the Time class
//compile usetime3.cpp and mytime3.cpp together
#include <iostream>
#include "mytime3.h"

int main()
{
using std::cout;
using std::endl;
Time aida(3, 35);
Time tosca(2, 48);
Time temp;

cout << "Aida and Tosca:\n";
cout << aida<<"; " << tosca << endl;
temp = aida + tosca; // operator+()
cout << "Aida + Tosca: " << temp << endl;
temp = aida - tosca; // operator+()
cout << "Aida - Tosca: " << temp << endl;
temp = aida* 1.17; // member operator*()
cout << "Aida * 1.17: " << temp << endl;
cout << "10.0 * Tosca: " << 10.0 * tosca << endl;
std::cin.get();
return 0;
}