COMP 110:Introduction to Programming

Tyler JohnsonApr 1, 2009

MWF 11:00AM-12:15PMSitterson 014

COMP 110: Spring 20092

Announcements

Lab 6 has been graded

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Questions?

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Today in COMP 110

Some Misc. Items

Multi-Dimensional Arrays

Programming DemoTicTacToe

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Program 4

Some comments

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Program 4

Extended to Friday at 5pm to better match the other section

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Lab 7

Some comments on the reverse/wheel methods

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Lab 6

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Multi-Dimensional Arrays

Section 7.5 in text

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2D Arrays

Arrays having more than one index are often useful

TablesGridsBingo games

0: Open 1: High 2: Low 3: Close

0: Apple Inc. 99.24 99.85 95.72 98.24

1: Walt Disney Co.

21.55 24.20 21.41 23.36

2: Google Inc. 333.12 341.15 325.33 331.14

3: Microsoft Corp.

21.32 21.54 21.00 21.50

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Creating 2D Arrays

//create a 2D array with 4 rows and 3 columnsint[][] table = new int[4][3];

or

int[][] table;table = new int[4][3];

99 99 95

21 24 21

333 341 325

21 21 21

rows

columns

Can be used to create a table that looks like this

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Creating 2D Arrays

int[][] table = new int[4][3];

gives you access to

table[0][0] //1st row, 1st columntable[0][1] //1st row, 2nd columntable[0][2] //1st row, 3rd column table[1][0]table[1][1]table[1][2]table[2][0]table[2][1]table[2][2]table[3][0] //4th row, 1st column table[3][1] //4th row, 2nd column table[3][2] //4th row, 3rd column

table[0][0]

table[0][1] table[0][2]

table[1][0]

table[1][1] table[1][2]

table[2][0]

table[2][1] table[2][2]

table[3][0]

table[3][1] table[3][2]

99 99 95

21 24 21

333 341 325

21 21 21

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Using 1D Arrays

We used a single loop to process a 1D array

int[] scores = { 13, 57, 93, 60, 102 };for(int i = 0; i < scores.length; i++) {

System.out.println(scores[i]);}

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Using 2D Arrays

When processing 2D arrays, we usually used two nested loops

int[][] table = new int[4][3];

//the outer loop iterates over the rowsfor(int row = 0; row < 4; row++) {

//the inner loop iterates over the columns for(int column = 0; column < 3; column++) { table[row][column] = 0;

}}

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Multi-Dimensional Arrays

You can have more than two dimensions

int[][][] table = new int[4][3][5];

Use more nested loops to access all elements

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Representation of 2D Arrays

int[] scores = new int[5];

“scores” is a one-dimensional arrayThe type of scores[0], scores[1] etc is int

int[][] table = new int[4][3];

Internally “table” is also represented as a one-dimensional array

The type of table[0], table[1] etc is int[] (an array!)We still refer to table as a two-dimensional array

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Representation of 2D Arrays

int[][] table = new int[4][3];

1 2 2

2 7 6

9 7 5

table[0]

table[1]

table[2]

table[3]

table

5 7 9

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Length field for 2D Arrays

int[][] table = new int[4][3];

table.length gives the number of rows (4 in this case)

table[0].length, table[1].length etc gives the number of columns (3 in this case)

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Multi-Dimensional Arrays as Parameters

//a method to print a 2D array to screenpublic void print2DArray(int[][] arr) {

for(int row = 0; row < arr.length; row++) {

for(int column = 0; column < arr[row].length; column++) { System.out.print(arr[row][column] + " "); }

System.out.println(); //jump to the next line after each row is complete }}

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Multi-Dimensional Arrays as Return Types

//create a 2D array of the specified size and return itpublic int[][] create2DArray(int rows, int columns) {

int[][] array = new int[rows][columns];

return array;}

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Programming Demo

TicTacToe

Create a class that allows the user to play a game of TicTacToe

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TicTacToe

Represent the game board as a 2D array of size 3x3

Type?• char

X O O

O X X

X X O

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Pseudocode

Until donedisplay game boarddisplay game menu (move, restart, quit)if(move)• ask where to move, update game board• if(winner || board full)

– done = true

else if(restart)• reset the game

else if(quit)• exit

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Decomposition

Public methodsConstructor

• sets everything upvoid play()

• starts the game

Private Methodsvoid displayBoard()

• Displays the entire game boardvoid displayRow(int row)

• Displays a single row of the game board• Used by displayBoard()

void displayMenu()• Displays the options menu to the user

boolean getMove()• Allows the user to update the game board by making a move• Returns true if the move resulted in a winner and false if not

boolean winner(int lastR, int lastC)• Checks if the move to lastR,lastC resulted in a winner• Used by getMove()

boolean boardFull()• Returns whether the board is full and the game is over

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Programming Demo

Programming

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Friday

Recitation

BringLaptop (fully charged)Textbook