AC21001 - Lab 2
A simple card game (twentyone)
© Glenn Rowe 2004
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The game of 21 (blackjack)
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Computer versus human
Use standard pack of cards
Deal 2 cards to each player
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one visible to both players
the other hidden - visible only to one player
Aim: get a score as near 21 as possible
without going over
Card values:
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Ace through 10  face value
Jack, Queen or King worth 10 each
© Glenn Rowe 2004
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The game of 21 (rules)
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Human has first turn
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decide whether to take one card or not
if not, human stands on cards held (cannot take
any more cards on future turns)
Computer turn is similar
Play continues until either:
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both players stand
one player goes over 21 (goes bust)
© Glenn Rowe 2004
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Classes
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Main classes:
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Card - a single card
Pack - the pack of cards
Player - computer or human
TwentyOne - runs the game play
© Glenn Rowe 2004
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Card class
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Card class
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represent one card in the pack
2 main properties:
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Rank can be int
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rank (ace, 2, 3, …Jack, Queen, King)
suit (spades, hearts, diamonds, clubs)
ace == 1, Jack == 11, Queen == 12, King == 13
Suit is string
Provide interface methods & ToString method
© Glenn Rowe 2004
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Pack class
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Pack class
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Can use array of Cards
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stores cards not yet used in play
must allow variable size
e.g. Card **cards for a Java-type array in C++
or use one of other methods in C++
Methods:
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Initialize (set pack to full 52 cards)
Shuffle
DealCard
© Glenn Rowe 2004
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Pack class - Initialize method
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Initialize card array - assign 52 cards to the
array
'cards' is a pointer to an array
of pointers, so initialize it with
cards = new Card*[52];
cards
00FE34D
new Card*[52]
00FE457 00FE519 00FE623
© Glenn Rowe 2004
[…]
[…]
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Pack class - Initialize method
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Initialize card array - assign 52 cards to the
array
Each pointer in the array must
then be initialized to a new
Card object.
E.g. for Ace of Spades:
cards
00FE34D
new Card*[52]
00FE457 00FE519 00FE623
[…]
[…]
cards[0] = new Card("Spade", 1);
[but use a loop for better efficiency!]
Spade
© Glenn Rowe 2004
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Pack class - Initialize method
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Initialize card array - assign 52 cards to the
array
Can access a card's suit with code
like this:
cards
00FE34D
string suit = card[0]->getSuit();
new Card*[52]
00FE457 00FE519 00FE623
Spade
© Glenn Rowe 2004
[…]
[…]
1
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Pack class - dealing cards
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Need to deal cards in random order
Two possibilities:
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If we select cards at random:
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select a card at random from an ordered pack
shuffle the pack and then deal cards in fixed order
need to mark a dealt card so it isn't selected again
when most of pack is dealt, need to generate a lot
of random numbers to find undealt card
Shuffling usually more efficient
© Glenn Rowe 2004
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Pack class - Shuffle method
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Various possibilities for shuffling algorithm
Easiest is probably:
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Pick 2 cards at random locations in the pack
Swap them
Repeat above steps several hundred times
© Glenn Rowe 2004
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Pack class - DealCard method
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If we have shuffled the pack:
Maintain a 'topOfPack' marker in Pack class
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To deal a card:
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records position of next card to be dealt
retrieve cards[topOfPack]
then decrement topOfPack
Remember to test if topOfPack >= 0
© Glenn Rowe 2004
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Player class
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Represents computer or human player
Requires:
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1 array for visible cards
Single Card variable for hidden card
or could also use an array to allow for game
variants
AddCard() method
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CardsValue() method
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adds a card to either visible or hidden array
calculates total value of all held cards
ToString() for printing player's details
© Glenn Rowe 2004
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Player class - card array
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Use same method as in Pack class for array
of cards
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use Card **visible
Allow array size that is large enough to hold a
reasonable selection of cards (say, 10)
AddCard should add a Card to 'visible' array
© Glenn Rowe 2004
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Player class - CardsValue( )
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CardsValue() totals up value of all cards held
(visible + hidden)
Use interface methods from Card class to
retrieve card's rank
Calculate value for each card and produce
sum
© Glenn Rowe 2004
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TwentyOne class
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TwentyOne class manages game play
Will need:
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One Pack object
Two Player objects (one for human, one for
computer)
In constructor:
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initialize Pack and Players
© Glenn Rowe 2004
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TwentyOne class - game play
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To start game:
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deal 2 cards to each player
one hidden, one visible
For human's turn:
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Ask if they want a card
If so, deal one (add to visible array)
If not, mark human as 'standing' so they cannot
ask for any more cards on later turns
© Glenn Rowe 2004
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TwentyOne class - game play
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Computer's turn:
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use your strategy to determine if computer takes a
card
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e.g. if holding > 15, stand; otherwise take card
or devise your own strategy
If computer takes card, add to visible list
If not, mark computer as 'standing'
© Glenn Rowe 2004
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TwentyOne class - end of turn
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After each turn:
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check total of cards held for player
if player has gone bust (> 21), game is over
if player has exactly 21, they win
After each pair of turns (human + computer):
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check if both players are 'standing'
if so, game is over…calculate totals for both
players
player closest to 21 wins
if scores equal, game is a draw
© Glenn Rowe 2004
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Destructors, copy constructors, =
operators
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For each class containing dynamic memory:
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Optionally:
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write a destructor
provide a copy constructor for each class
and an overloaded = operator
Follow examples in lectures / notes
Once you've done one, the rest should be
much the same
© Glenn Rowe 2004
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main( ) function
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main() should create a TwentyOne object
Then offer user the option of playing as many
games as they like (use a loop as in nim lab)
© Glenn Rowe 2004
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Optional extras - double-valued ace
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In full rules, the ace can be worth either 1 or
11
Modify your program to allow this
Creates possibility of a player being dealt a
'natural' 21
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ace + 10-valued card
© Glenn Rowe 2004
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Optional extras - scoring / betting
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Keep score (how many wins, losses and
draws for each player)
or…
Introduce a simple betting system
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e.g. each player bets a certain amount at each
turn in the game
after each game, winner takes all
or split the total amount 50/50 for a draw
© Glenn Rowe 2004
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Optional extras - computer strategy
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Do a bit of research on web
Find out statistics for when it's best to take an
extra card and when to stand
Incorporate these into your program
© Glenn Rowe 2004
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