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11.5. Yet another example

The original version of convertToSeconds looked like this:

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

It is straightforward to convert this to a member function:

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

The interesting thing here is that the implicit parameter should be declared const, since we don’t modify it in this function. But it is not obvious where we should put information about a parameter that doesn’t exist. The answer, as you can see in the example, is after the parameter list (which is empty in this case).

The print function in the previous section should also declare that the implicit parameter is const.

Feel free to try out the convertToSeconds() function in the active code below!

#include <iostream> using namespace std; struct Time { int hour, minute; double second; double convertToSeconds () const; void print (); }; int main() { Time currentTime = { 9, 14, 30.0 }; double secs = currentTime.convertToSeconds(); cout << "The current time is "; currentTime.print(); cout << "." << endl; cout << "This time in seconds is " << secs << "." << endl; } ==== void Time::print () { cout << hour << ":" << minute << ":" << second; } double Time::convertToSeconds () const { int minutes = hour * 60 + minute; double seconds = minutes * 60 + second; return seconds; }

Q-2: When writing a member function, where should you declare the implicit parameter to be const?

• Before the parameter list.
• Incorrect! Try again!
• Inside the parameter list.
• Incorrect! This would be correct if we were talking about a free-standing function.
• After the parameter list.
• Correct!
• Implicit parameters are always const and don't need to be declared.
• Incorrect! Parameters are only const if they are not modified inside the function, implicit parameters are no exception.

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