As an example using arrays, let s write some code to get started with the Upthrust game. We can use a 2D array to represent the game board.

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1 Array Example Upthrust Board As an example using arrays, let s write some code to get started with the Upthrust game. We can use a 2D array to represent the game board. First, note that the game board is 4 columns and 11 rows. We can nicely represent this using a 2D array. We ll use the convention that 0,0 is the lower left corner and 3,10 is the upper right corner: 10: : : : : :.... 4:.... 3: G R B Y 2: R B Y G 1: B Y G R 0: Y G R B The contents of the array can be a char representing the color as R, G, B, Y or if there is nothing in the cell. To write in a little more English-like code, we can use some constants to represent the entries on the board (using Visual Studio, below): #include <iostream> using namespace std; const char BLANK = '.'; const char RED = 'R'; const char BLUE = 'B'; const char GREEN = 'G'; const char YELLOW = 'Y'; const char ROWS = 11; const char COLUMNS = 4; void initboard(char board[][rows]); int main() char board[columns][rows]; initboard(board); system("pause"); void initboard(char board[][rows]) for (int y = 0; y < ROWS; y++) board[x][y] = BLANK;

2 board[0][0] = YELLOW; board[1][0] = GREEN; board[2][0] = RED; board[3][0] = BLUE; board[0][1] = BLUE; board[1][1] = YELLOW; board[2][1] = GREEN; board[3][1] = RED; board[0][2] = RED; board[1][2] = BLUE; board[2][2] = YELLOW; board[3][2] = GREEN; board[0][3] = GREEN; board[1][3] = RED; board[2][3] = BLUE; board[3][3] = YELLOW; return; We can run this but there is no way to see if it works! The next thing to do is to make a function that can display the board. Here is our first version that outputs a board like that shown on the previous page. Our first little complication is that if the row is less than 10 then we should print a space before the digit (e.g. 9 so it lines up under 10 ). We can do this using setw(2) which sets the width of the field to always be 2 characters. To get access to setw we must include iomanip: #include <iomanip> void displayboard(char board[][rows]) cout << " " << "." << " "; If we call this from main after initializing the board we get: We can add in the scoring values on the right and read from the array instead of always printing a dot: void displayboard(char board[][rows]) cout << " " << board[x][y] << " "; if (y == 10) cout << " 60";

3 if (y == 9) cout << " 40"; if (y == 8) cout << " 30"; if (y == 7) cout << " 20"; if (y == 6) cout << " 10"; cout << " " << endl; Our board now looks like this! We can also use arrays to represent the colors assigned to the players. We ll use index 0 for player 1 and index 1 for player 2. We can make an array that maps from the player number to the colors assigned for that player, and another array that goes the other way around. In this example player 1 has been assigned Red and Blue while player 2 has been assigned Green and Yellow: const char PLAYER1 = 0; const char PLAYER2 = 1; char playertocolor[2][2]; // first index = player number, second = slot for color playertocolor[player1][0] = RED; // P1 = RED, BLUE playertocolor[player1][1] = BLUE; playertocolor[player2][0] = YELLOW; // P2 = YELLOW, GREEN playertocolor[player2][1] = GREEN; We will find it useful to map from a color to which player it is. We can define a function for this purpose: int colortoplayer(char color, char playertocolor[][2]) if (playertocolor[player1][0] == color) if (playertocolor[player1][1] == color) // If it wasn't player 1 then it must belong to player 2 return PLAYER2;

4 Armed with these new functions let s update our display function so it prints out the colors for player 1 in lowercase and the colors for player 2 in uppercase: void displayboard(char board[][rows], char playertocolor[][2]) if (colortoplayer(board[x][y], playertocolor) == PLAYER1) cout << static_cast<char>(tolower(board[x][y])); else cout << board[x][y]; if (y == 10) cout << " 60"; if (y == 9) cout << " 40"; if (y == 8) cout << " 30"; if (y == 7) cout << " 20"; if (y == 6) cout << " 10"; cout << " " << endl; The function tolower() converts to lowercase, but returns its value as an int. This is why we typecast it back to a char! Our last function for now is to compute the score of the board. It returns the score for a particular player: int score(int player, char board[][rows], char playertocolor[][2]) int total = 0; int rowvalue = 10; for (int y = 6; y <= 10; y++) if (board[x][y]!= BLANK) if (colortoplayer(board[x][y], playertocolor) == player) total += rowvalue; if (y == 9) return total; We can test this by manually reconfiguring the board to put some pieces in scoring position: board[0][6] = YELLOW; board[1][0] = GREEN; board[2][0] = RED; board[3][0] = BLUE; board[0][1] = BLUE; board[1][7] = YELLOW; board[2][7] = GREEN; board[3][1] = RED; board[0][2] = RED; board[1][2] = BLUE; board[2][2] = YELLOW; board[3][2] = GREEN;

5 board[0][3] = GREEN; board[1][10] = RED; board[2][8] = BLUE; board[3][3] = YELLOW; Test code in main: cout << "Player 1 " << score(player1, board, playertocolor) << endl; cout << "Player 2 " << score(player2, board, playertocolor) << endl; Here is the final result: For your reference here is the final code (with the board reset to the initial state): #include <iostream> #include <iomanip> using namespace std; const char BLANK = '.'; const char RED = 'R'; const char BLUE = 'B'; const char GREEN = 'G'; const char YELLOW = 'Y'; const char ROWS = 11; const char COLUMNS = 4; const char PLAYER1 = 0; const char PLAYER2 = 1; void initboard(char board[][rows]); void displayboard(char board[][rows], char playertocolor[][2]); int colortoplayer(char color, char playertocolor[][2]); int score(int player, char board[][rows], char playertocolor[][2]); int main() char board[columns][rows]; color char playertocolor[2][2]; // first index = player number, second index = slot for playertocolor[player1][0] = RED; playertocolor[player1][1] = BLUE; playertocolor[player2][0] = YELLOW; // P1 = RED, BLUE // P2 = YELLOW, GREEN

6 playertocolor[player2][1] = GREEN; initboard(board); displayboard(board, playertocolor); cout << "Player 1 " << score(player1, board, playertocolor) << endl; cout << "Player 2 " << score(player2, board, playertocolor) << endl; system("pause"); void initboard(char board[][rows]) for (int y = 0; y < ROWS; y++) board[x][y] = BLANK; board[0][0] = YELLOW; board[1][0] = GREEN; board[2][0] = RED; board[3][0] = BLUE; board[0][1] = BLUE; board[1][1] = YELLOW; board[2][1] = GREEN; board[3][1] = RED; board[0][2] = RED; board[1][2] = BLUE; board[2][2] = YELLOW; board[3][2] = GREEN; board[0][3] = GREEN; board[1][3] = RED; board[2][3] = BLUE; board[3][3] = YELLOW; return; void displayboard(char board[][rows], char playertocolor[][2]) if (colortoplayer(board[x][y], playertocolor) == PLAYER1) cout << static_cast<char>(tolower(board[x][y])); else cout << board[x][y]; if (y == 10) cout << " 60"; if (y == 9) cout << " 40"; if (y == 8) cout << " 30"; if (y == 7) cout << " 20"; if (y == 6) cout << " 10"; cout << " " << endl; int colortoplayer(char color, char playertocolor[][2]) if (playertocolor[player1][0] == color) if (playertocolor[player1][1] == color) // If it wasn't player 1 then it must belong to player 2 return PLAYER2;

7 int score(int player, char board[][rows], char playertocolor[][2]) int total = 0; int rowvalue = 10; for (int y = 6; y <= 10; y++) if (board[x][y]!= BLANK) if (colortoplayer(board[x][y], playertocolor) == player) total += rowvalue; if (y == 9) return total;