One last example

Section 1.10 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 1.10.1. 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;
}

Checkpoint 1.10.2.

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Checkpoint 1.10.3.

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You have attempted of activities on this page.

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