TCPP2 One last example

Section 11.9 One last example

The final example we’ll look at is addTime:

Time addTime2(const Time& t1, const Time& t2) {
  double seconds = convertToSeconds(t1) + convertToSeconds(t2);
  return makeTime(seconds);
}

We have to make several changes to this function, including:

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Change the name from addTime to Time::add.
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Replace the first parameter with an implicit parameter, which should be declared const.
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Replace the use of makeTime with a constructor invocation.
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Here’s the result:

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Time Time::add(const Time& t2) const {
  double seconds = convertToSeconds() + t2.convertToSeconds();
  Time time(seconds);
  return time;
}

The first time we invoke convertToSeconds, there is no apparent object! Inside a member function, the compiler assumes that we want to invoke the function on the current object. Thus, the first invocation acts on this; the second invocation acts on t2.

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The next line of the function invokes the constructor that takes a single double as a parameter; the last line returns the resulting object.

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Listing 11.9.1. Feel free to try out the add function in this active code!

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#include <iostream>
using namespace std;

struct Time {
    int hour, minute;
    double second;
    Time(double secs);
    Time(int h, int m, double s);
    bool after(const Time& time2) const;
    Time add(const Time& t2) const;
    double convertToSeconds() const;
    void print();
};

int main() {
    Time t1(9, 20, 0.0); cout << "t1 = "; t1.print(); cout << endl;
    Time t2(7, 30, 0.0); cout << "t2 = "; t2.print(); cout << endl;
    Time t3 = t1.add(t2);
    cout << "Time t1 + Time t2 = "; t3.print(); cout << endl;
}
====
Time::Time(double secs) {
  hour = int(secs / 3600.0);
  secs -= hour * 3600.0;
  minute = int(secs / 60.0);
  secs -= minute * 60.0;
  second = secs;
}

Time::Time(int h, int m, double s) {
  hour = h; minute = m; second = s;
}

void Time::print() {
  cout << hour << ":" << minute << ":" << second;
}

double Time::convertToSeconds() const {
  int minutes = hour * 60 + minute;
  double seconds = minutes * 60 + second;
  return seconds;
}

Time Time::add(const Time &t2) const {
  double seconds = convertToSeconds() + t2.convertToSeconds();
  Time time(seconds);
  return time;
}

bool Time::after(const Time& time2) const {
  if (hour > time2.hour) return true;
  if (hour < time2.hour) return false;

if (minute > time2.minute) return true;
  if (minute < time2.minute) return false;

if (second > time2.second) return true;
  return false;
}

Checkpoint 11.9.1.

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Checkpoint 11.9.2.

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You have attempted of activities on this page.

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