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:

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

Here’s the result:

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.

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

Feel free to try out the add function in the active code below!

#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;
}

Before you keep reading...

Runestone Academy can only continue if we get support from individuals like you. As a student you are well aware of the high cost of textbooks. Our mission is to provide great books to you for free, but we ask that you consider a $10 donation, more if you can or less if $10 is a burden.

Support Runestone Academy Today

You have attempted 1 of 4 activities on this page