The C++Course provides a general introduction to programming in C++. It is based on A.B. Downey's book, How to Think Like a Computer Scientist. Click here for details.


The next function I want to write is find, which searches through a vector of Cards to see whether it contains a certain card. It may not be obvious why this function would be useful, but it gives me a chance to demonstrate two ways to go searching for things, a linear search and a bisection search.

Linear search is the more obvious of the two; it involves traversing the deck and comparing each card to the one we are looking for. If we find it we return the index where the card appears. If it is not in the deck, we return -1.

int find (const Card& card, const pvector<Card>& deck) {
  for (int i = 0; i < deck.length(); i++) {
    if (equals (deck[i], card)) return i;
  return -1;

The loop here is exactly the same as the loop in printDeck. In fact, when I wrote the program, I copied it, which saved me from having to write and debug it twice.

Inside the loop, we compare each element of the deck to card. The function returns as soon as it discovers the card, which means that we do not have to traverse the entire deck if we find the card we are looking for. If the loop terminates without finding the card, we know the card is not in the deck and return -1.

To test this function, I wrote the following:

  pvector<Card> deck = buildDeck ();

  int index = card.find (deck[17]);
  cout << "I found the card at index = " << index << endl;

The output of this code is

I found the card at index = 17

Last Update: 2005-12-05