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Problem
Write a program that uses an array to store the results of a simulation with two n-sided dice. At each step in the simulation, “roll” the pair of the dice and use the array to keep track of the number times each of the possible sums has been rolled so far. To store the results of the simulation, you will need an array of length 2n - 1, where n is the number of sides to each die. The following is an example of what an array for two 6-sided dice could look like after a 24-step simulation.
0 1 2 3 4 5 6 7 8 9 10
1 3 0 2 3 5 3 4 2 1 0
Element 0 in our array represents a sum of 2, element 1 represents a sum of 3 and so on.
The above array indicates that during the simulation, a sum of 2 (element 0) was rolled
once, while a sum of 7 (element 5) was rolled 5 times.
Your program should ask the user for two values:
• The number of sides to the dice. Both dice will have the same number of sides.
• The number of steps in the simulation.
After reading in the input using Scanner, simulate rolling the die by generating two random
numbers between 1 and the number of sides (inclusive). After the simulation is complete,
print out a histogram displaying the percentage of simulation steps that generated each
possible sum. You may re-use code from A3 to print the histograms.
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Solution
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Code
Solution Code
insert solution code here
import java.util.Scanner;
/**
* A4Q1 -
*
* COMP 1010 Section A00
* INSTRUCTOR
* ASSIGNMENT 4, Question 1
* @author 1010
* @version 2010-Dec-3
*
* PURPOSE: simulation with two n-sided dice
*/
public class A4Q1 {
public static void main(String[] args) {
// declare variables
int[] rollArray;
Scanner myScanner = new Scanner(System.in);
int numSides;
int numSteps;
// get the number of sides
System.out.println("Enter the number of sides to the dice");
numSides = myScanner.nextInt();
// allocate the memory for the array
rollArray = new int[2*numSides - 1];
// get the number of steps
System.out.println("Enter the number of simulation steps");
numSteps = myScanner.nextInt();
while(numSteps != -1) {
// initialize all elements of the array to 0
initializeArray(0, rollArray);
// perform the simulation
performSimulation(numSides, rollArray, numSteps);
// print the histogram
printRollHistogram(numSides, rollArray, numSteps);
// get the next number of simulation steps
System.out.println("Enter the number of simulation steps");
numSteps = myScanner.nextInt();
}
System.out.println("Programmed by [your name here].\nEnd of Processing.");
}
/**
* Set all array elements to an initial value
*
* @param initValue The initial value
* @param array The array of integers
*
*/
public static void initializeArray(int initValue, int[] array) {
for(int i = 0; i < array.length; i++) {
array[i] = initValue;
}
}
/**
* Generate a random number between 1 and a maximum number (inclusive)
*
* @param maximum The maximum number to generate
* @return A random number between 1 and maxium (inclusive)
*/
public static int generateRandomNumber(int maximum) {
int number = (int)(Math.random()*(maximum) + 1); // generate a random number between 1 and maximum
return number;
}
/**
* Perform the simulation by rolling the dice a number of times
*
* @param numSides The number of sides to the dice
* @param counts An array containing the number of times each sum was rolled
* @param numSteps The number of steps in the simulation
*
*/
public static void performSimulation(int numSides, int[] counts, int numSteps) {
int roll1;
int roll2;
for(int i = 1; i<=numSteps; i++) {
roll1 = generateRandomNumber(numSides);
roll2 = generateRandomNumber(numSides);
counts[roll1 + roll2 - 2]++;
}
}
/**
* Print out the histogram
*
* @param numSides The number of sides to the dice
* @param counts An array containing the number of times each sum was rolled
* @param numSteps The number of steps in the simulation
*
*/
public static void printRollHistogram(int numSides, int[] counts, int numSteps) {
int percentage;
System.out.println("Results of a "+ numSteps + "-step simulation with two " + numSides + "-sided dice: ");
for(int i = 0; i < counts.length; i++) {
percentage = (int)Math.round(counts[i] / ((double) numSteps) * 100);
if(i < 8) {
printBar("Sum of " + (i+2), percentage, '=');
}
else {
printBar("Sum of " + (i+2), percentage, '=');
}
}
}
/**
* Prints out a single bar for a histogram.
*
* @param label the label this bar should use
* @param percent the number of symbols the bar should have
* @param barSymbol the character the bar uses to indicate 1%
*/
public static void printBar(String label, int percent, char barSymbol) {
// works well when all labels are the same width, but not so well otherwise.
System.out.print(label + ": ");
for (int i = 0; i < percent; i++) {
System.out.print(barSymbol);
}
System.out.println(" (" + percent + "%)");
}
}
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