ENGR/CS 101 CS Session Lecture 11 Log into Windows (reboot if in - - PowerPoint PPT Presentation

Lecture 11 ENGR/CS 101 Computer Science Session 1

ENGR/CS 101 CS Session Lecture 11

 Log into Windows (reboot if in Linux)  Use web browser to go to session webpage

http://csserver.evansville.edu/~hwang/f11-courses/engrcs101/cs.html

 Right-click on Inclass11.zip link. Save

link/target to Visual Studio 2010 projects folder.

 Browse to Inclass11.zip, right-click on it and

select Extract All... and extract project folder

 Double-click into the ConwaysLife folder, then

double-click on the Visual Studio Solution file.

Lecture 11 ENGR/CS 101 Computer Science Session 2

Outline

 Cellular automata  Conway's Game of Life  C# GUI implementation of the game

 Two-dimensional arrays

Lecture 11 ENGR/CS 101 Computer Science Session 3

Cellular Automata

 A cellular automaton is used in discrete

• modeling. It consists of a regular grid of cells,

each of which can be in one of a finite number

• f states.

 Time is discrete, so the state of a cell at time

t+1 is a function of the state of a finite number

• f neighboring cells at time t.

 A rule (or function) is applied to every cell at

each time step and all updates happen at once creating a new generation.

Lecture 11 ENGR/CS 101 Computer Science Session 4

Conway's Game of Life

 Conway's Game of Life is one well-known

example of a two-state, two-dimensional cellular automaton.

 The cells are square, and the neighborhood is

the 8 cells immediately adjacent (i.e., including diagonally) to a cell.

 At each generation, a cell may be live

(represented by a '*' in the cell) or dead (represented a space cell).

Lecture 11 ENGR/CS 101 Computer Science Session 5

Conway's Game of Life

 The original rules posed by Conway are:

 If a live cell has fewer than 2 live neighbors, the cell

dies of loneliness

 If a live cell has more than 3 live neighbors, the cell

dies of overcrowding

 If a dead cell has exactly 3 live neighbors, the cell

becomes alive by birth

 Otherwise, the cell state is unchanged

Lecture 11 ENGR/CS 101 Computer Science Session 6

Conway's Game of Life

 Here is an example of how the rule works using

the interface mockup for a GUI implementation

• f Conway's.

 An initial condition is shown below.

Lecture 11 ENGR/CS 101 Computer Science Session 7

Conway's Game of Life

 The figure below shows the number of live

neighbors each cell has in the initial condition.

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Conway's Game of Life

 Applying the rules, the end live cells have only one

neighbor, so they die. Two new cells are born above and below the center live cell as they have 3 live

• neighbors. The center live cell has two neighbors so it

continues to live. The resulting state is shown below.

Lecture 11 ENGR/CS 101 Computer Science Session 9

Interface Mockup

 The interface mockup shown consists of

 Two textboxes, one for the number of generations

to be computed when the Next button is clicked and

• ne for the time between generation updates.

 Two buttons, one to start the next generation

updates and one to reset the simulation state back to the way it is when the program first starts.

 A grid of labels that represent the cells of the grid

that are dynamically created when the application starts.

Lecture 11 ENGR/CS 101 Computer Science Session 10

Implementation

 All of the interface and most of the code for the

game has been provided to you. The parts of the code (press F7 to see it) that you need to understand to finish the implementation are as follows.

Lecture 11 ENGR/CS 101 Computer Science Session 11

Implementation

 Data Items:

 genCount – an integer that keeps track of the

number of generations that have been simulated. The value of this integer is displayed in generationCount.Text

 grid – a 2-D array of Labels currently set to 10 rows

and 20 columns that are displayed by the GUI.

 nextGrid – a 2-D array of strings the same size as

grid used to hold the state of the cell in the next generation.

Lecture 11 ENGR/CS 101 Computer Science Session 12

Two-dimensional Arrays

 A two-dimensional (2-D) array is a data

structure that represents a 2-D grid of

• elements. Generally, the first dimension index

is called the row index and the second dimension index is called the column index.

[0] [1] [2] [3] [4] [5] [0] [1] [2] [3] Column Indexes Row Indexes

Lecture 11 ENGR/CS 101 Computer Science Session 13

Two-dimensional Arrays

 An individual element is accessed by giving an

index for each dimension. In C#, the indexes are given as a list of indexes separated by

• commas. E.g. grid[0,0] is the element with row

index of 0 and column index of 0, i.e., the upper left corner element.

Lecture 11 ENGR/CS 101 Computer Science Session 14

Two-dimensional Arrays

 Often we want to access every element in a

2-D array, e.g. to initialized the elements to some value like 0 or a space. This is usually done by nesting two for-loops to count each

• index. In C#, the code for this would look like:

int rowMax = grid.GetUpperBound(0), colMax = grid.GetUpperBound(1); for (int i=0; i < rowMax; i++) for (int j=0; j < colMax; j++) { // do something with grid[i,j] }

Lecture 11 ENGR/CS 101 Computer Science Session 15

Implementation

 Algorithm elements

 Function CountNeighbors receives the row and

column indexes of a grid element (called i and j) and returns the number of live neighbors that surround grid[i,j]. The neighboring elements have indexes that are one more and one less for both the row and column index, but the function also must check that the resulting index is still a valid one.

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Implementation

 We will implement the functions whose stubs

are at the bottom of the code file.

 grid_Click - handler for when a grid label is clicked  clear_Click - handler for the Clear button  ComputeGenerations - a function that implements

the game rules

Lecture 11 ENGR/CS 101 Computer Science Session 17

grid_Click

 grid_Click is the handler for the grid labels. We

want to alternate between "*" and a space. The

• nly tricky part is we need to tell the compiler to

treat the sender argument as a Label like so:

Label cell = (Label) sender;

 Otherwise the algorithm is simple

• 1. If cell.Text is a "*" then

1.1 Set cell.Text to a space (" ") Else (cell is a space) 1.2 Set cell.Text to "*"

 Try running the program and clicking in a cell.

Lecture 11 ENGR/CS 101 Computer Science Session 18

clear_Click

 clear_Click is the handler for the Clear button.

It simply sets all of the grid cells to a space and resets the generation counters to 0.

• 1. Declare and initialize rowMax to grid.GetUpperBound(0)
• 2. Declare and initialize colMax to grid.GetUpperBound(1)
• 3. Loop index i from 0 to rowMax by 1

3.1 Loop index j from 0 to colMax by 1 3.1.1 Set grid[i,j].Text to a space

• 4. Set genCount to 0
• 5. Set generationCount.Text to "0"

 Try running the program and clicking the Clear

button after clicking in some grid cells.

Lecture 11 ENGR/CS 101 Computer Science Session 19

ComputeGenerations

 ComputeGenerations is the function that

embodies the game rules. It uses the CountNeighbors function to determine the number of neighbors a cell has, then applies the rules to compute the cell state in the next generation.

 Since all of the next states must be computed

before a cell can be changed, the auxiliary grid nextGrid is used to hold the results. These are transfered back to grid in the DisplayGeneration function.

Lecture 11 ENGR/CS 101 Computer Science Session 20

ComputeGenerations

 Implement the steps shown in bold:

• 1. Declare and initialize rowMax to grid.GetUpperBound(0)
• 2. Declare and initialize colMax to grid.GetUpperBound(1)
• 3. Loop index i from 0 to rowMax by 1

3.1 Loop index j from 0 to colMax by 1 3.1.1 Compute neighbors = CountNeighbors (i, j) 3.1.2 If grid[i,j].Text is "*" and neighbors is less than 2 or greater than 3 then 3.1.2.1 Set nextGrid[i,j] to a space (i.e., a death) 3.1.3 Else if grid[i,j].Text is " " and neighbors is 3 then 3.1.3.1 Set newGrid[i,j] to "*" (i.e., a birth) 3.1.4 Else (no change) 3.1.4.1 Set newGrid[i,j] to grid[i,j].Text 3.2 Increment genCount

Lecture 11 ENGR/CS 101 Computer Science Session 21

Check This Out!

 Try the following initial condition.