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Representing a Game Board

Representing a Game Board. In a game, we represent the action taking place using an array In a very simple game, we use individual variables to represent where players might be on the game board (like our GameBoard example from earlier)

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Representing a Game Board

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  1. Representing a Game Board • In a game, we represent the action taking place using an array • In a very simple game, we use individual variables to represent where players might be on the game board (like our GameBoard example from earlier) • For more complex games, we store all of the values in an array • in tic tac toe requires that we know where each X and O have been stored • in chess, we need to know in which square every piece currently resides • in a card game, we have to store each card dealt to the player • So we will use arrays to represent the game board and any special situations

  2. Tic-Tac-Toe • We can represent tic-tac-toe as a 3x3 game board of chars (‘X’, ‘O’, ‘ ’ or ‘b’) • char[ ][ ] ttt = new char[3][3]; • The user will input their next move as two values, for instance, 2, 2 to represent the middle square, or 1, 3 to represent the middle row, rightmost square • If they are entering values from 1-3,1-3, we have to subtract 1 from each – why? Or we can make them enter values from 0-2 and 0-2 • We can also represent tic-tac-toe as a 1D array from 0-8 as shown below • Which is easier?

  3. Tic Tac Toe Logic • For this game, you need to do the following • Create the board • Repeat until someone has won or the game is a draw (you can keep track of this by counting turns, if turn = 9, then the board is filled) • Draw the board on the screen • Get player 1’s guess and data verify that the guess is within bounds (0-2, 0-2, or 1-3, 1-3 if you prefer, or between 0 and 8) and that the square is empty (ttt[row][col]==‘ ’) or (ttt[row][col]==‘b’) if you are using b for blank (empty) square • Check to see if player 1 has won the game with this move • Otherwise, repeat with player 2 (get pick, data verify, check for win) • Output the winner

  4. Human vs Computer Version • If you want to play against the computer, you replace player 2 with the computer generating a move • How does the computer make a pick? • Randomly – just generate a number from 0-8 (or two numbers from 0 to 2) • Try to win/not to lose – check to see if player 1 can win on next move, if so, block, else check to see if player 2 can win on next move, if so use it, else randomly generate move • Strategy – pick center square if available, else pick whichever corner is available, else pick a middle square • Combine “try to win” with “strategy” for the best computer version • For a real elaborate program, ask the user to input a skill level (0 for random, 1 for try to win, 2 for strategy, 3 for combined)

  5. How do you check for a win? • This depends on whether you have used the 2D or 1D array version • If 2D, you want to compare all 3 squares of a row to see if they are the same and are all Xs or Os • Testing row 0: • if(ttt[0][0]==ttt[0][1]&&ttt[0][0]==ttt[0][2]&&(ttt[0][0]==‘X’||ttt[0][0]==‘O’)) … • Do the same for [1][0], [1][1], [1][2] and [2][0], [2][1], [2] • How do you test for a column? • if(ttt[0][0]==ttt[1][0]&&ttt[0][0]==ttt[2][0]&&(ttt[0][0]==‘X’||ttt[0][0]==‘O’)) … • How do you test for the two diagonals? • If you are using the 1D array, its pretty much the same but you have to figure out the indices for each row, column and diagonal • Testing column 0: • if(ttt[0]==ttt[3]&&ttt[0]==ttt[6]&&(ttt[0]==‘X’||ttt[0]==‘O’))…

  6. Another Game: Battleship • In the game of battleship, two players play on 10x10 grids • Each player places their ships somewhere on the grid • Then, players take guessing where a ship might be by calling out coordinates such as 5, 7 • If the other player has a ship at 5, 7, they announce “hit” else they announce “miss” • If you hit a player’s ship, you try to destroy it by hitting it at all coordinates. For instance, a submarine covers 3 grid positions, perhaps at 5, 6, and 5, 7, and 5, 8 • So if found at 5, 7, you would check 4, 7, and 6, 7 or 5, 6 and 5, 8 and then try another neighboring position until you have destroyed it • NOTE: ships must either be placed horizontally or vertically, not diagonally, and ships cannot go off the 10x10 grid or overlap each other • Ship sizes vary depending on type: aircraft carriers are 5 grid positions long, battleships 4, submarines and destoyers 3, and patrol boats 2 • The player who has destroyed all of the other player’s ships wins the game

  7. Our Battleship Game • Since you and another player cannot both look at the screen (you would see each other’s setup), we will implement a Battleship solitaire game • The computer will randomly position 5 ships on the 10x10 grid – have to make sure that no ships overlap and no ships run off the screen (see the logic in two slides) • Iterate until either you have sunk all of the computer’s ships, your number of picks have elapsed, or you get sick of playing and want to quit • Get the user’s next pick and increment the number of picks • Check to see if that pick is legal (between 0 and 9) • Check to see if the pick is a hit (if so, mark it so in the array) or a miss • If a hit, see if it sinks a ship (has the ship been hit in every position?)

  8. The Battlefield • The battlefield will be a 10x10 array of char’s • Each element should store • ‘ ’ if that position has no ship in it and hasn’t been guessed yet • ‘a’-’e’ if that position is part of a boat and hasn’t been guessed yet where the boats are labeled ‘a’ for aircraft carriers, ‘b’ for battleships, ‘c’ for submarines, ‘d’ for destroyers, and ‘e’ for patrol boats • ‘m’ if the user has guessed that position and it is a miss • ‘h’ if the user has guessed that position and it is a hit • ‘s’ if the user has sunk that boat by hitting all parts of it • The array is originally declared to be all ‘ ’ and then the computer randomly generates which boats go into which of the slots, so before the game starts, the board is all ‘ ’, ‘a’, ‘b’, …, ‘e’ • While the game is in session, the computer changes squares to store ‘h’, ‘m’ and ‘s’ as needed

  9. Computer Placing Ships • This is the trickiest part of the program • We have to make sure that the computer places the 5 boats such that none overlap and none go off the board • One strategy is as follows: • First select horizontal or vertical • Next, select a starting point between 0 and 10 – shipsize • for instance, a battleship could go from 10 – 4 = 6 onward (6 to 9) in either the horizontal or vertical direction • Verify that this does not intersect another ship and if so, try again • Another tricky part of the game is determining if a ship has been sunk • You can do this by having five variables, one for each boat type, initialized to 5, 4, 3, 3 and 2 • For each hit, decrement the appropriate variable based on the ship type and then if that variable is 0, you have sunk that ship

  10. Random generator = new Random(); int i, red, green, blue; int[] x, y, size; Color[] color; x = new int[25]; y = new int[25]; size = new int[25]; color = new Color[25]; for(i=0;i<25;i++) { x[i]=generator.nextInt(480) + 10; y[i]=generator.nextInt(480) + 10; size[i]=generator.nextInt(10) + 3; red=generator.nextInt(256); green=generator.nextInt(256); blue=generator.nextInt(256); color[i]=new Color(red, green, blue); } g.setColor(Color.black); g.fillRect(0,0,500,500); for(i=0;i<25;i++) { g.setColor(color[i]); g.fillOval(x[i], y[i], size[i], size[i]); } Storing Graphics Data in an Array • We use 4 arrays • x, y for the <x, y> coordinate • size for the size of the oval • color to store the Color of the oval

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