CSE 131 Module 4: Input & Output

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Extensions

Extension 1: Create an Instrument (6 points):

Authors

Warm Up

• Update your repository and locate the instrument package in the extensions folder.
• You will find a copy of PlayThatTune in the instrument package, credited to Sedgewick's book, as this code is adpated from Sedgewick's PlayThatTune.
• Run PlayThatTune and verify that it plays the music files correctly.

Overview

• For the purposes of this work, let's define a frequency factor as a multiplicative factor to be applied to a frequency f:

  In the example below, let's assume that f is 440 Hz (cycles per second), which is concert A. On a piano, this is the A above middle C:

  • a factor of 1 results in the same frequency as f, because 1*f==f.
  • a factor of 2 yields a frequency an octave higher than f.

    For this example, we obtain 880 Hz, which is the A above high C on a piano:

    
  • a factor of 4 yields a frequency two octaves higher than f.

    Here we obtain 1760 Hz, an octave above the A above high C:

    
  • a factor of 3 is between one and two octaves higher, and it turns out to be one octave plus a just (or, pure) fifth above the pitch corresponding to f. Here we obtain the frequency 1320 Hz, which sounds like the E above high C. The sound is slightly different than on a piano, where the pitches are not perfect but are instead evenly spaced apart from each other. The corresponding note on the piano has a frequency of 1318.51 Hz, slightly flatter than what we get by our frequency factor.
  • a factor of 0.75 (ratio of 3:4) yields a note that sounds like an E, but dividing by 4 lowers its pitch by two octaves. With f at concert A, a frequency factor of 3:4 yields a frequency of 330, whichsounds like the E above middle C: Again, the pitch on a piano is slightly different; in this case it is slightly flatter at 329.63.

• It is thus convenient to specify a frequency factor as the ratio of two integers. In the above examples we see 1:1, 2:1, 4:1, 3:1, and 3:4.
• To build an actual instrument, we must pick the frequency factors we wish to hear, and specify how strong each should be. The table below specifies such an instrument:

  Frequency Factor		Relative
  Numerator	Denominator	Strength
  1	1	1
  2	1	0.75
  3	2	0.50

  The first row is the fundamental frequency. The second is an octave higher, and is 3/4 as strong as the fundamental frequency. The third row specifies a pitch that is a fifth above the fundamental freqnecy, and quieter still at half the strength of the fundamental frequency.

  The waveform that results from such an instrument specification is shown below in red, with the three frequency factors shown in black:

  

  • The red solid waveform is literally the sum of the black dotted waveforms. The sound you produce is sampled from the red waveform, and that is the subject of this extension.
  • The plot shown above is not the subject of this extension, but is shown to help explain how complex sounds are built from simple ones, as follows:
    • The black waveform with the largest amplitude (the tallest black waveform) is the fundamental frequency at relative strength 1. The sample shown is for 1/440 of a second of a 440 Hz concert-A. This is sufficient ot show one full cycle of the fundamental frequency.
    • The black waveform with the next largest amplitude has relative strength 0.75. It is an octave higher, so it oscillates twice in the timespan of the fundamental pitch's waveform.
    • The black waveform of smallest amplitude (at half the strength of the fundamental frequency) is the 3:2 frequency factor, which sounds like a fifth above the fundamental frequency. As expected, it exhibits 1.5 cycles in the timespan of the fundamental pitch's waveform.
  • The sound of the red waveform, which is what you will produce below, is similar to an oboe or a clarinet (in the opinion of my son).

Procedure

1. First prompt the user for how many frequency factors the user wishes to specify. In the above example, 3 such frequencies were used.
2. For each frequency factor, prompt the user for its
   • Numerator (an int)
   • Denominator (an int)
   • Relative strength (a double)

   The information about the frequency factors must be saved (in arrays) for future use.

3. The code in PlayThatTune, copied with attribution from PlayThatTune, reads in a file and computes a value in a variable called hz that is the fundamental frequency of the tune being played.

   The hz value is computed from concert A (440 Hz), taking the specified number of equally spaced chromatic steps above (or below) concert A.

   The relevant details, explained in the lecture slides for this module, are not necessary to complete this extension, but please ask if you would like clarification.

4. Your task is to modify the assignment to the sample a[i] in the provided code: The sine wave sampled and assigned there is for:
   • the fundamental frequency (hz, shown in the red box) of the desired pitch
   • relative strength 1.0 (the result of the sine function call is implicitly multiplied by 1, shown at the red dot).

   In place of that value, you must compute the sum of sine wave samples, one for each frequency factor, as follows:

   • a[i] is initially zero.
   • For each frequency factor f_k, add to a[i] a sample obtained as follows:
     • The value passed to the sine function must be multiplied by the frequency factor. This means multiplying the red-boxed hz by the ratio of the numerator and denominator of the frequency factor.
     • The value returned from the sine function must be multiplied by the relative strength of the frequency factor. This happens at the red dot.
5. Test your program on the A.txt file first, which is a single note. Then try Ascale.txt and some other songs.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.1

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 1

Extension 2: Draw a Sound Wave (10 points):

Authors

Warm Up

You will modify your program further in this extension to produce the sine-wave plots that depict how sine-wave addition occurs.

The details of this assignment are not completely specified so that you must think through what is needed to produce meaningful plots. Ask for help as needed!

Procedure

• An example of a plot is shown below:
  • The black waveform with the largest amplitude (the tallest black waveform) is the fundamental frequency at relative strength 1. The waves shown are for 1/440 of a second of a 440 Hz concert-A. This is sufficient ot show one full cycle of that fundamental frequency.
  • The black waveform with the next largest amplitude has relative strength 0.75. It is an octave higher, so it oscillates twice in the timespan of the fundamental pitch's waveform, at 880 Hz.
  • The black waveform of smallest amplitude (at half the strength of the fundamental frequency) is 660 Hz: the 3:2 frequency factor, which sounds like a fifth above the fundamental frequency. As expected, it exhibits 1.5 cycles in the timespan of the fundamental pitch's waveform.
  • The red waveform is the sum of the black ones.
• Each of the frequency factors incorporated into an instrument is shown separately by plotting dots of the curve as the values are computed.
• With frequencies on the order of hundereds or thousands of cycles per second, we must limit the time of the plot so that we can see one or two cycles clearly.

  Think about how many samples you need to capture to show one complete cycle at 440 Hz.

  One way to reason about this is to use the units of the various computations and multiply or divide them to obtain the property you seek.

• Plot the individual waveforms using black dots, as shown above.
• Plot the summation waveform using red connected line segments, as shown above.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.2

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 2

Extension 3: Loud or Graphics-ful Bouncing Balls (2 points):

Authors

Extension points available for Lab 4

Trevor Larsen and Tyler Spinks submitted this video for your amusement, as a demo of this extension. It is based on the John Cena Prank Call video.

If you have added sound or pictures to your solution for Lab 4, demo those to a TA and receive points for this extension.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.3

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 3

Extension 4: Magic 8 Ball (7 points):

Authors

• Ron K. Cytron

A video demonstrating my solution can be found here.

The Magic Eight Ball is an autoresolution device. A question of boolean type is posed, the Magic Eight Ball is turned over, and it then displays its advice in a murky window. It has resurfaced in other guises over the ages, most recently perhaps as The Magic Conch Shell in the Club SpongeBob episode of SpongeBob SquarePants.

To receive credit for this extension, your implementation of the Magic 8 Ball must:

• Repeatedly prompt the user for his or her question using ArgsProcessor.
• Dramatically cause the answer to emerge in a (StdDraw) display, over a 2-5 second period, as follows:
  • Display the result in a triangular shape, such as shown here. (Your solution will be much more dramatic as you include the following.) Your triangle need not rotate.
  • Your rendering must fade the image from black to showing the triangle with text in a continuous manner, as the answer emerges.
  • Your rendering of the answer must cause the text go from blurry to sharp as the answer emerges.
  • Try to have a suitably eerie sound accompany your display. (not necessary for credit, but nice)

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.4

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 4

Extension 5: Roving Eyes (10 points):

Authors

• Ron K. Cytron
• Ken Goldman

A video demonstrating my solution can be found here.

This extension has been brought back from the 131 vaults, having originally been conceived by Ken Goldman, formerly a professor in our department and currently at Google. In its new form, it has been rewritten to comform to Sedgewick's API. Also, it does not make use of objects, so it can be offered as an extension at this point in the course.

Although the solution can be quite short (mine weighed in at approximately 50 lines), there are some tricky aspects to this work, and it may be an extension that you work on over several weeks.

You will have to interact with the mouse, perhaps for the first time, both in terms of its location and determining whether the mouse has been pressed and released. It will take patience to get this to work, but most students like the end result.

The idea

• Each time the mouse is clicked, an eyeball is deposited on the image.
• Each eyeball consists of two parts:
  • An outer filled circle that is white with a thin black border. This part of the eyeball does not move as the mouse moves around the screen.
  • An inner filled circle with of some color (mine are red, below). This part of the eyeball does move, so that the eyeball can appear to be looking at something.
• All eyeballs seem to look at the mouse, wherever the mouse moves within the StdDraw window.

This is the initial image you should draw. The picture can be found as images/ken.jpg in your workspace.	Here, I have clicked over the image to deposit my first eyeball. The mouse (not shown) is to the right, so the eyeball is looking that way.	Then I clicked a second time to deposit another eyeball, this time over the right eye shown in the image. Both eyeballs are looking at my mouse, which is at the lower right (not shown).	Each time I click the mouse, another eyeball is deposited, and all eyeballs continue looking at my mouse, wherever it happens to be.

Part 0: Initialize your application

• Begin by drawing the picture in the image.
• Prompt the user to specify the maximum number of eyeballs that will be drawn. This information is necessary so that you can appropriately provision arrays needed to implement this extension.

This code is included in your repository. Open the extensions folder in which you will find the eyeballs package. Open and run the Eyeballs class.

Part 1: Detecting mouse clicks

Unfortunately, in Sedgewick's API, we can only determine the current status of a mouse button as up or down. We must then use logic and iteration to discover whether a mouse has been pressed, released, or clicked. This low-level API for the mouse leads to some mixed feelings about how you are learning to interact with the mouse:

• The code you write will not be typical of how most Java programs interact with the mouse. The reason for this is that your work takes place in an infinite loop, slowed only by the use of StdDraw.pause(n), which consumes resources on your computer even when you are not moving the mouse.
• You are essentially polling the mouse as to whether it is up or down, and then using your own logic to determine whether it has been pressed, released, clicked, or dragged. From a pedagogical perspective, you will learn how this kind of processing takes place at a low level on some computers. You also learn how to track the state of an input device over time, and many applications require this kind of logic.

Following is a description of mouse actions as they are typically used in most applications:

Mouse press

We think of this as a single push-down action on a mouse or trackpad. This action usually initiates some activity in applications.

From an application's point of view, this event happens just once when the mouse is pushed down. Generation of another mouse press action would require the mouse to be released, and then pressed again.

Mouse release

If a mouse has been pressed, then it can be released. Some applications distinguish between the press and release, so that the mouse can move between those actions. This is sometimes called dragging the mouse.

Mouse click

While this is a compound action, consisting of a mouse press followed by a mouse release, it is usually treated as an atomic action that takes place at exactly one coordinate. The release also happens within some reasonable timeframe of the press, if the press and release are to be construed as a click.

The above mouse actions are the logical ones that we wish to implement. Actually, it suffices for this extension to determine only a mouse release, but you are welcome to think about how to discover the other actions.

The Sedgwick API offers only the following interface, which we must use in our application to simulate the above mouse actions.

double mouseX()

returns the x-coordinate of the mouse, expressed in terms of the coordinates of the StdDraw canvas.

double mouseY()

returns the y-coordinate of the mouse, expressed in terms of the coordinates of the StdDraw canvas.

boolean mousePressed()

A better name for this would be boolean isMouseDown(), because this method does not detect a mouse press in the standard view of mouse actions. Instead it simply reports whether the mouse button is currently pressed or not.

Your task is to simulate a mouse-click action using the above API. This will inevitably involve polling the mouse as to whether the button is down or up. Consider the following code:

while (!StdDraw.mousePressed()) {
    // do nothing, 
    // we are waiting for the mouse button to go down  
    //
    // The line below is important, as described below
    //
    StdDraw.show(50);
}

• Without the pause using StdDraw.show(50), this application would run in a tight loop that would always keep your computer busy, even if you are not interacting with the application. As a result, all of the other applications open on your computer would suffer from not getting sufficient CPU resources to be reponsive. These applications would appear to behave sluggishly.
• Sedgewick uses the pause intervals to hide updates that you make to the drawing canvas. Between calls to show, no updates are shown. At the call to show, the screen is redrawn, and the CPU is released for the specified period of time (50 milliseconds in the above code).

Make sure your eyeballs are depositing properly as you mouse-click before you move on to implement more features.

Part 2: Following the mouse movement

A pupil within an eyeball tracks objects using the geometry of similar triangles. The following diagram and discussion may be useful.

• The eyeball is centered at (ex,ey) and is looking at the object (the mouse) at (mx,my). This leads to the following equations:
  • mx = ex + dx
  • my = ey + dy
• Knowing (ex,ey) and (mx,my), we can solve for dx and dy.
• Knowing dx and dy, we can compute d using the distance formula.
• We know p, because it is the radius of the eyeball minus the radius of the pupil. This may be hard to see, but convince yourself of this by looking carefully at the figure.
• The green triangle is similar to the large triangle.
• Knowing p and d, we can compute their ratio.
• That same ratio describes px:dx py:dy.
• From those ratios we can compute px and py.
• Knowing (ex,ey), px, and py, we can compute the center of the red pupil as (ex+px,ey+py).

Putting it all together

Give yourself time for this extension, and develop and test the aspects in the order described above.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.5

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 5

Extension 6: Roving Eyes; Slow Motion Edition (5 points):

Authors

• Ron K. Cytron
• Ken Goldman

• We suggest that you wait until you have completed module 5 to do this extension, as the information in module 5 will help.
• A video demonstrating a solution can be found here.

You are not allowed to do this by slowing the simulation down. Instead, you must smoothly vary where the eyes should look in the normal speed of the simulation.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.6

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 6

Extension 7: Web Scraper (3 points):

Authors

• Fede Rozenberg
• Ron K. Cytron

Intro

Web scrapers are programs that search websites and scrape off useful data. You will write a web scraper in this assignment that looks for weather information in a zip code of interest. There are two ways to go about this:

• The result of accessing a web URL is a stream of text which you can receive a a Java String. You can scan that String for information of interest. In this approach, you search for features that delimit the area of interest, and trim the String to extract data of interest.
• A library has been developed for Java called jsoup that allows direct interaction with a website's HTML. This library regards a web document in terms of its structure. You use methods from this library to navigate to the part of the web page that is of interest.

URLs and web sites

• Watch this video which demonstrates how URLs are used in the http://www.wunderground.com/ web site.
• We have to reverse engineer how that web site uses URLs to request zip-code-specific weather information.

  Reverse engineering skills are useful skills and can serve you well.

  • After watching the video, visit the http://www.wunderground.com/ site
  • Take a look around for a bit to see what is offered there
  • Type into the field Search Locations some zip code of interest to you. Examples might include
    • 63130 for Washington University
    • 80424 for Breckenridge, Colorado
    • 10598 for Yorktown Height, New York
  • Observe that when you submit your request, you are taken to a web page whose URL is different from the home page for the site.
• Try editing the URL in your browser to find weather information for a different zip code of interest to you.
• For one or more of the pages you reach, view the source of that web page in your browser, as you saw in the video.

  Browsers vary in how they allow you to see the page source. If you are on the web page of interest, try control- (right-) clicking and one option you should see should resemble View Page Source.

  If you are lost, try Googling for how to view page source in your browser.

• Try to locate the text within the page source that corresponds to the temperature report. In the video, this was found near the string curTemp in the source.

Simple use of jsoup

• Watch this video which shows how to supply jsoup with a URL within Java.
• The result of that interaction is a String.

Procedure

• Find and open the Weather class in the scraping project of your extensions folder.
• That code is what you saw on the video, with comments added to direct your work.
• Your task is essentially to isolate the temperature data and some other statistic from the source text of the web page.

  • What makes this difficult is that the author of the web page doesn't know you want to find this information.
  • You have to look at the web page yourself to find distinguishing features of the page near where you want to extract information.
  • Worse still, the author of that web page is not obligated to keep the information you see in future versions of that web page. Scraping is a dodgy effort at best, and you may have to revise your code in response to changes made by the author of the pages you scrape.

• It will be helpful to use some methods from the String class. The following describes some of those methods, assuming they are called on a target String t.

  int indexof(String str)

  Finds the location of the specified str in t.

  String substring(int beginIndex)

  Returns a new String that is copied from t, starting at the supplied beginIndex.

  String substring(int beginIndex, endIndex)

  Returns a new String that is the substring of t, starting at the supplied beginIndex, up to but not including endIndex.

Demo

• Complete the code as instructed in the comments.
• Your output must include the current temperature and some other statistic of interest from that same web page.
• Show the output to your TA.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.7

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:

End of extension 7

Extension 8: Stock Scraper (0 points):

Authors

• Tim Heyer
• Ron Cytron

It is highly recommended that you complete the easyStrings assignment before attempting this assignment.

Additionally, this assignment builds off of the Web Scraper assignment and it is recommended that you complete that assignment prior to attempting this one. If you decide to work on this assignment without having completed the former, it is, however, necessary that you watch the two videos provided in the Web Scraper assignment in order to fully understand this assignment.

Overview

In this assignment, you will access the Yahoo! Finance website, store the HTML code of the website in a String, and extract the current stock price of a company (along with some other useful information). You will use the API provided through Jsoup to download and store the HTML code of the website, which you learned how to do through the aforementioned Web Scraper assignment videos. Once you've stored the HTML code of the website in a String, you will then analyze the code to find the relevant information and come up with a unique identifying String which will allow you to extract the stock information.

Procedure

• Use ArgsProcessor to prompt user for the stock ticker input.
• Use Jsoup to retrieve the HTML code of the Yahoo! Finance website and store it as a String.
• Look at the HTML source code (as described in the previous assignment's videos) and create Strings that will allow you to identify and then extract the relevant stock information.

  Specifically, you are looking for three different pieces of information that you will extract and print.

  • The full name of the company in question.
  • The current price of the stock.
  • The % daily change in stock price. (This is provided as its own element in the HTML code and therefore does not require any computation on your part)

• It will be helpful to use some methods from the String class. The following describes some useful methods, assuming they are called on a target String t:

  int indexof(String str)

  Returns the location of the specified str in t.

  char charAt(int i)

  Returns the character at index i in t.

• Three particular static methods may also be useful for this assignment. Recall that static methods are not called on a target variable as in the previously described methods, but rather are called on a generic object of that type.

  boolean Character.isDigit(char c)

  Returns true if c is a digit and false otherwise.

  String Character.toString(char c)

  Returns the String representation of a character.

  int Integer.parseInt(String s)

  Returns the int representation of a String.

Example

Input: INTC

Stock information for Intel Corporation
The stock most recently opened at $31.87
The current stock price is $31.88 which is a -0.38% change today.

Demo

• Show your TA the output and run the program with multiple different stock tickers.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.8

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

---

TA: Password:


End of extension 8

---

Extension 9: temp: easyStrings (0 points):

Authors

• Tim Heyer

This extension should be placed before all other web scraping extensions

Overview

The purpose of this assignment is to give you the skills to index and analyze Strings in order to prepare for different web scraping tasks. Once you are able to extract information of interest from a String, you will be ready to query a webpage, save the raw HTML code, and extract relevant information.

For this assignment, you are given two different arithmetic expressions as Strings. Your task is to extract the two integer values and the arithmetic operator from each String and save them as variables of their respective type. You will then compute and print the value of the expression.

Example

Given: String s = "2 + 3";

You must first extract 2 and 3 to int variables and + to a char or String variable. Then you will compute and print the expression 2+3=5

Procedure

• As previously mentioned, the purpose of this assignment is to prepare you for dynamic web scraping tasks. As such, it is expected that you implement this assignment dynamically. In other words, the only assumption you should have about the String you are analyzing is that it will be in the format (Positive Integer)(Arithmetic Operator)(Positive Integer). This implies your implementation should be able to run effectively on an expression containing positive integers of any length. It should also be able to effectively extract any arithmetic operator (+, -, *, /) and print the proper answer.

  It is important to note that there are many acceptable ways to implement this assignment. It is up to your discretion which way you choose to implement the procedure as long as it abides by the requirements described above.

• You should begin by extracting the first integer value from the String using the methods described below.
• Once you've figured out how to extract the first integer, you should implement a similar approach for the second integer and the operator, in conjunction with String indexing functions.
• Now that you have the two integers in int variables and the operator in a char or String variable, you can perform and print the simple arithmetic operation.
• It will be helpful to use some methods from the String class. The following describes some useful methods, assuming they are called on a target String t:

  int indexof(String str)

  Returns the location of the specified str in t.

  char charAt(int i)

  Returns the character at index i in t.

• Three particular static methods may also be useful for this assignment. Recall that static methods are not called on a target variable as in the previously described methods, but rather are called on a generic object of that type.

  boolean Character.isDigit(char c)

  Returns true if c is a digit and false otherwise.

  String Character.toString(char c)

  Returns the String representation of a character.

  int Integer.parseInt(String s)

  Returns the int representation of a String.

Demo

• Be prepared for your TA to review your code and change the digits and operator in the String you are analyzing to ensure your implementation is dynamic.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.9

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

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TA: Password:


End of extension 9

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Extension 10: Gambler's Ruin with CSV File (0 points):

Authors

• Jarett Gross

This assignment is a continuation of the Gambler's Ruin assignment from Module 2. You must first complete and demo that assignment before you can demo this assignment.

Background

In this assignment, you will export the data that you received from your Gambler's Ruin simulation to a Comma Separated Values (CSV) file. These types of files can be opened with programs like Microsoft Excel. CSV files store tabular data as regular text, where each entry in the data is separated from another entry by a comma and each line of a CSV file is a data record.

Procedure

1. Alter your program to take numberOfWinChances as an input, which specifies how may different winning chances to simulate. Then, accept that many win chances as inputs. Finally, simulate the Gambler's Ruin totalPlays times for each winChance.

   Think of a way to store these values, as you will be using them throughout your program.

2. Next, create an array to store strings for each row of your CSV. As you simulate the Gambler's Ruin, store the chance of winning, the number of rounds played for one simulation, and the result of that simulation. Each of these groups of variables are one row of your CSV file.
3. Use Java's FileWriter class to create the CSV file and write your data to that file.

   You must import java.io.FileWriter to use this class.

4. Use a try- catch block and instantiate an object of type FileWriter, which takes a String of the path name to your file. An example path name would be: outputs/fileName.csv
   Use the append method to write the strings contained in your CSV array to the file. Then, once you are finished writing strings to the file, use the close method to close and flush the stream.

   Remember that each line in your CSV file is its own row. How can you use the append method and your array to write multiple rows to the CSV file?

5. Your CSV file when opened with Excel should look similar to this:

   startAmount	stopAmount	winChance	rounds	results
   12	18	0.1	14	LOSE
   12	18	0.1	14	LOSE
   12	18	0.1	12	LOSE
   12	18	0.4	18	LOSE
   12	18	0.4	46	LOSE
   12	18	0.4	18	LOSE
   12	18	0.7	14	WIN
   12	18	0.7	44	WIN
   12	18	0.7	8	WIN

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.10

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

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TA: Password:


End of extension 10

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Extension 90: AJAX Web Scraping (0 points):

Authors

• Tim Heyer

Overview

This assignment explores how to scrape some more advanced and dynamic webpages than we've seen previously. Specifically, it focuses on identifying when AJAX requests are being utilized by a website and how to extract relevant information from the page.

AJAX, or Asyncronous Javascript and XML, is a web technology that allows a website to request data from a server in the background (asyncronously) in order to provide a more rich and dynamic experience for the end user. Since all communication with the server happens behind the scenes, the webpage that the user sees and interacts with becomes faster and doesn't need to refresh nearly as often.

By retrieving data and updating the page without refreshing, however, our ability to scrape the page simply by modifying the URL is forfited. As a result, we are forced to get a bit more creative in our scraping approach. It turns out that it is, in fact, possible to scrape these pages and just requires some research and digging on our part.

Analyzing AJAX Requests

• Watch this video which explains AJAX requests in more detail and demonstrates how to scrape a simple, AJAX-based weather widget.

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.90

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

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TA: Password:


End of extension 90

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Extension 100: Nutrition Again (C++) (8 points):

Authors

• Dan Nolan

For this extension you will re-use your nutrition code from Lab 1, and potentially the C++ code you wrote from the similar extension. The difference is that this time instead of writing the information to terminal, you will use a file to write out the nutrition info and the analysis. You will then demonstrate your ability to read back in that file.

By completing this work, you demonstrate that you can:

• Utilize the input/output features of C++
• Incorporate new headers into existing work
• Produce meaningful output based on your computations

Procedure

1. First, create a nutritionFSteam C++ source and header file in the nutrition package of the extensions source folder.
2. Think about the information you need to write to the file, where you want white space, or where you do not. You should also think about which Data Type you should use for your information in order to write them out correctly.
3. Consider making it as simple as possible to avoid unnecessary coding when you read it back in.

You will need to prompt the user for inputs just as before and calculate the same boolean values and caloric values

You will need to initailize a ofstream which stands for output file stream

You will also need to initialize a ifstream which stands for input file stream

Arrange for your program to produce output such that:

• It prompts the user for nutritional data from food
• It prompts the user for a file name to save under
• It writes out the file correctly, and read's in the file correctly
Finally, your program should print the same exact information as it did before, but this time reading it from your file stream rather than printing them out from your code directly.

 

When you done with this extension, you must be cleared by the TA to receive credit.

• Commit all your work to your repository
• Fill in the form below with the relevant information
• Have a TA check your work
• The TA should check your work and then fill in his or her name
• Click OK while the TA watches
• If you request propagation, it does not happen immediately, but should be posted in the next day or so

This demo box is for extension 4.100

	Last name	WUSTL Key	Propagate?
		(or your numeric ID)		Do not propagate
e.g.	Smith	j.smith
1				Copy from 1 to all others
2				Copy from 2 to all others

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TA: Password:


End of extension 100

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