This is a simulation of rolling dice. Actual results approach theory only when the sample size is large. So we will need to repeat rolling the dice a large number of times (we will use 10,000). The theoretical probability of rolling doubles of a specific number is 1 out of 36 or approximately 278 out of 10,000 times that you roll the pair of dice. Since this is a simulation, the numbers will vary a little each time you run it.

Check out how to use the random number generator (introduced in Section 4.11 of the text) to get a number between 1 and 6 to create the simulation.

We will continue to use control structures that we have already learned, while exploring control structures used for repetition. We shall also continue our work with algorithms, by translating a given algorithm into java code, in order to complete our program. We will start with a while loop, then use the same program, changing the while loop to a do-while loop, and then a for loop.

We will be introduced to file input and output. We will read a file, line by line, converting each line into a number. We will then use the numbers to calculate the mean and standard deviation.

First we will learn how to use file output to get results printed to a file. Next we will use file input to read the numbers from a file and calculate the mean. Finally, we will see that

when the file is closed, and then reopened, we will start reading from the top of the file again so that we can calculate the standard deviation.

Task #1 The while Loop

1.Copy the file DiceSimulation.java (see Code Listing 4.1) from the Student Files

or as directed by your instructor. DiceSimulation.java is incomplete. Since

there is a large part of the program missing, the output will be incorrect if you run

DiceSimulation.java.

2. I have declared all the variables. You need to add code to simulate rolling the dice and keeping track of the doubles. Convert the algorithm below into Java code and place it in the main method after the variable declarations, but before the output statements. You will be using several control structures: a while loop and an if-else-if statement nested inside another if statement. Use the indenting of the algorithm to help you decide what is included in the loop, what is included in the if statement, and what is included in the nested if-else-if statement.

3. To roll the dice, use the nextInt method of the random number generator to generate an integer from 1 to 6.

Repeat while the number of dice rolls are less than the number of times the dice should be rolled.

Get the value of the first die by rolling the first die

Get the value of the second die by rolling the second die

If the value of the first die is the same as the value of the second die If value of first die is 1

Increment the number of times snake eyes were rolled Else if value of the first die is 2

Increment the number of times twos were rolled Else if value of the first die is 3

Increment the number of times threes were rolled Else if value of the first die is 4

Increment the number of times fours were rolled Else if value of the first die is 5

Increment the number of times fives were rolled Else if value of the first die is 6

Increment the number of times sixes were rolled Increment the number of times the dice were rolled

4. Compile and run. You should get numbers that are somewhat close to 278 for each of the different pairs of doubles. Run it several times. You should get different results than the first time, but again it should be somewhat close to 278.

Task #2 Using Other Types of Loops

1. Change the while loop to a do-while loop. Compile and run. You should get the same results.

2. Change the do-while loop to a for loop. Compile and run. You should get the same results.

Task #3 Writing Output to a File

1. Copy the files StatsDemo.java (see Code Listing 4.2) and Numbers.txt from the Student Files or as directed by your instructor.

2. First we will write output to a file:

a- Create a PrintWriter object passing it the name of the file. (Dont forget the needed import statement).

b- Since you are using a PrintWriter object, add a throws clause to the main method header.

c- Print the mean and standard deviation to the output file using a three decimal format, labeling each.

d- Close the output file.

3- Compile, debug, and run. You will need to type in the filename Numbers.txt. You should get no output to the console, but running the program will create a file called Results.txt with your output. The output you should get at this point is: mean = 0.000, standard deviation = 0.000. This is not the correct mean or standard deviation for the data, but we will fix this in the next tasks.

Task #4 Calculating the Mean

1- Now we need to add lines to allow us to read from the input file and calculate the mean.

a- Create a Scanner object passing it, passing it a File object with the name of the file.

2- Write a loop that continues until you are at the end of the file.

3- The body of the loop will:

a- read a double value from the file

b- add the value to the accumulator

c- increment the counter

4- When the program exits the loop close the input file.

5- Calculate and store the mean. The mean is calculated by dividing the accumulator by the counter.

6- Compile, debug, and run. You should now get a mean of 77.444, but the standard deviation will still be 0.000.

Task #5 Calculating the Standard Deviation

1- We need to reopen to the file so we can start reading from the top again.

a- Create a Scanner object passing it, passing it a File object with the name of the file.

2- Reinitialize sum to 0.

3- Reinitialize count to 0.

4- Write a loop that continues until you are at the end of the file.

5- The body of the loop will:

a- read a double value from the file

b- subtract the mean from the value, store the result in difference

c- add the square of the difference to the accumulator

d- increment the counter

6- When the program exits the loop close the input file.

7- The variance is calculated by dividing the accumulator (sum of the squares of the difference) by the counter. Calculate the standard deviation by taking the square root of the variance (Use the Math.sqrt method to take the square root).

8- Compile, debug, and run. You should get a mean of 77.444 and standard

deviation of 10.021.

Code Listing 4.1 (DiceSimulation.java)

import java.util.Random; // Needed for the Random class

/**

This class simulates rolling a pair of dice 10,000 times and counts the number of times doubles of are rolled for each different pair of doubles.

*/

public class DiceSimulation

{

public static void main(String[] args)

{

final int NUMBER = 10000; // Number of dice rolls

// A random number generator used in

// simulating the rolling of dice Random generator = new Random();

int die1Value; // Value of the first die int die2Value; // Value of the second die int count = 0; // Total number of dice rolls int snakeEyes = 0; // Number of snake eyes rolls int twos = 0; // Number of double two rolls

int threes = 0; // Number of double three rolls int fours = 0; // Number of double four rolls int fives = 0; // Number of double five rolls int sixes = 0; // Number of double six rolls

// TASK #1 Enter your code for the algorithm here

// Display the results

System.out.println ("You rolled snake eyes " +

snakeEyes + " out of " + count + " rolls.");

System.out.println ("You rolled double twos " +

twos + " out of " + count + " rolls.");

System.out.println ("You rolled double threes " +

threes + " out of " + count + " rolls.");

System.out.println ("You rolled double fours " +

fours + " out of " + count + " rolls.");

System.out.println ("You rolled double fives " +

fives + " out of " + count + " rolls.");

System.out.println ("You rolled double sixes " +

sixes + " out of " + count + " rolls.");

}

}

Code Listing 4.2 (StatsDemo.java)

import java.util.Scanner;

// TASK #3 Add the file I/O import statement here

/**

This class reads numbers from a file, calculates the mean and standard deviation, and writes the results to a file.

*/

public class StatsDemo

{

// TASK #3 Add the throws clause public static void main(String[] args)

{

double value = 0; double sum = 0; int count = 0; double mean = 0; double stdDev = 0; double difference;

// To hold a value from the file

// The sum of the numbers

// The number of numbers added

// The average of the numbers

// The standard deviation

// The value and mean difference

// Create an object of type Scanner

Scanner keyboard = new Scanner (System.in); String filename; // The user input file name

// Prompt the user and read in the file name System.out.println("This program calculates " +

"statistics on a file " + "containing a series of numbers");

System.out.print("Enter the file name: ");

filename = keyboard.nextLine();

// ADD LINES FOR TASK #4 HERE

// Create a Scanner object passing it a File object

// with the name of the file.

// Loop until you are at the end of the file

// Read a double value from the file

// Add the value to sum

// Increment the counter

// After the loop finishes, close the input file

// Store the calculated mean in the mean variable

/// ADD LINES FOR TASK #5 HERE

	// // // // // // // // // // //	Create a Scanner object passing it a File object with the name of the file. Reinitialize sum to 0 Reinitialize count to 0 Loop until you are at the end of the file Read a double value from the file subtract the mean from the value Add the square of the difference to the sum Increment the counter After the loop finishes, close the input file Store the calculated standard deviation in stdDev
	// // // //	ADD LINES FOR TASK #3 HERE Create a PrintWriter object using "Results.txt" Print the results to the output file Close the output file
} }