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How To Think Like a Computer Scientist C++ Edition The Pretext Interactive Version

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:
  1. Change the name from addTime to Time::add.
  2. Replace the first parameter with an implicit parameter, which should be declared const.
  3. 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.
Listing 11.9.1. Feel free to try out the add function in this active code!

Checkpoint 11.9.1.

Checkpoint 11.9.2.

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