13.8. Subdecks¶
How should we represent a hand or some other subset of a full deck? One
easy choice is to make a Deck object that has fewer than 52 cards.
We might want a function, subdeck, that takes a vector of cards and
a range of indices, and that returns a new vector of cards that contains
the specified subset of the deck:
Deck Deck::subdeck (int low, int high) const {
Deck sub (high - low + 1);
for (size_t i = 0; i < sub.cards.size(); i++) {
sub.cards[i] = cards[low + i];
}
return sub;
}
To create the local variable named subdeck we are using the Deck
constructor that takes the size of the deck as an argument and that does
not initialize the cards. The cards get initialized when they are copied
from the original deck.
The length of the subdeck is high - low + 1 because both the low card
and high card are included.
Warning
This sort of computation can be confusing and can lead to “off-by-one” errors. Drawing a picture is usually the best way to avoid them.
As an exercise, write a version of findBisect that takes a subdeck
as an argument, rather than a deck and an index range. Which version is
more error-prone? Which version do you think is more efficient?
Try writing the findBisect function in the commented section
of the active code below. If done correctly, the program should output that
the Seven of Clubs is at index 6 and the King of Diamonds is at index -1.
If you get stuck, you can reveal the extra problem at the end for help.
Let’s write the code for this version of the findBisect function. findBisect should take a subdeck and a card as parameters and return the index of the card in the subdeck or -1 if it’s not found.