C++ Operator Overloading （操作符重载）

Operator overloading is an example of C++ polymorphism.

class header file:

// mytime0.h -- Time class before operator overloading
#ifndef MYTIME0_H_
#define MYTIME0_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

class definition file:

// mytime0.cpp -- implementing Time methods
#include <iostream>
#include "mytime0.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 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
{
std::cout << hours << " hours, " << minutes << " minutes";
}

class main file:

// usetime0.cpp -- using the first draft of the Time class
// compile usetime0.cpp and mytime0.cpp together
#include <iostream>
#include "mytime0.h"

int main()
{
using std::cout;
using std::endl;
Time planning;
Time coding(2, 40);
Time fixing(5, 55);
Time total;
Time diff;
Time adjusted;

cout << "planning time = ";
planning.Show();
cout << endl;
cout << "coding time = ";
coding.Show();
cout << endl;
cout << "fixing time = ";
fixing.Show();
cout << endl;
total = coding+fixing; // use operator+()
cout << "fixing time + coding time = ";
total.Show();
cout << endl;
diff = fixing - coding; // use operator-()
cout << "fixing time - coding time = ";
diff.Show();
cout << endl;
adjusted = total * 1.5; // use operator*()
cout << "adjusted work time = ";
adjusted.Show();
cout << endl;

return 0;
}

The result is:

planning time = 0 hours, 0 minutes
coding time = 2 hours, 40 minutes
fixing time = 5 hours, 55 minutes
fixing time + coding time = 8 hours, 35 minutes
fixing time - coding time = 3 hours, 15 minutes
adjusted work time = 12 hours, 52 minutes