Lab 4

Loops and Methods 🧑‍🔬

Labs provide hands-on experience with course material. They have three parts: review questions, guided exercise, open-ended exercise.

The first few Labs provide practice with fundamentals, and the later Labs go hand-in-hand with the term project check-ins.

Tips are at the very bottom. You should read them.

Part 1/3: Review Questions

Answer the following questions from our course textbook. If you have trouble getting a copy of the book, email me and check the KCTCS libraries. Type your answers all the way out – don't just say "a" or "b" or etc.

• Chapter 4, Review Questions: 4, 5, 6, 7, 8, and 12
• Chapter 4, Exercises: 1
• Chapter 6, Review Questions: 2, 6, 9, 10, 11, 12, and 13

Also answer these questions:

1. How does our textbook define "desk checking"?
2. This is a common coding interview question: Desk check the following logic, and explain what this code has the computer do. How many times will it output the word "FizzBuzz"? Explain your reasoning. (Note: I am not asking you to run this code, I am asking you to explain it yourself by hand. This really is a common interview question.)

   i = 1
   while i <= 50
       if i % 15 == 0
           output "FizzBuzz!"
       elseif i % 5 == 0
           output "Buzz!"
       elseif i % 3 == 0
           output "Fizz!"
       else
           output i
       endif
   endwhile

3. How does the book define "scope?" What logic errors does it mention related to this?
4. Send me an email that says hello
5. Story Problem: ACME Corp. released the following code by mistake. All the lines got scrambled! Put the code back in the correct order and add proper indentation. There is only one correct order.

   return $result;
   function multiply($a, $b) {
   }
   $result = $a * $b;

6. (Come back and answer this question after completing the rest of the assignment) What problems, if any, did you encounter at any point in this Lab? What did you do to overcome them?

Part 2/3: Guided Exercise

Let's practice making and calling methods in your assigned language. See Journal 9 for examples.

Regular Reminder: Be familiar with my plagiarism policy. Also avoid Google, as the results it gives will be out of scope for where we are in this class. Instead, use the documentation sites I linked to in Lab 1 Part 2.

First, create a void method with no parameter inputs. Call it displayCopyrightInfo. Inside it's logic, just have it display a minimal copyright text.

Run your code to make sure it compiles and you have no syntax errors. You shouldn't see any output yet, since you haven't called your method yet. Embed a screenshot of your code at this point.

For example:

Regular Reminder: My examples in Julia show the flow of logic and expected results in the Console pane. My examples will NOT have the same syntax as yours. Practice separating (a) the flow of logic for solving a problem in general from (b) the nitty gritty of different programming syntaxes.

Second, if you are using an interpreted language, call your method at the bottom of your code. If you are using a compiled language, call your method inside your main. Run it again and take another screenshot. For example:

Third, modify displayCopyrightInfo so that it takes one integer parameter, year. And modify it so that it inserts that variable into the message it displays.

Fourth, update your call in your "main" so that it calls displayCopyrightInfo(2020) instead. Then copy and paste that line a few times so it prints a copyright message for the years 2019, 2020, and 2021. Run and take another screenshot. For example:

Fifth, create a method that will return a number/double. Call it addTaxRate. Have it accept two number/double parameters, subtotal and rate. Inside its logic, just have it compute the total by multiplying subtotal with rate, then return the total.

Sixth, call addTaxRate(10, 1.07) in your main. You should not see any output yet, since we have not told the program to print anything about that method. Run and take another screenshot. For example:

Seventh, capture the return value of that method in your main with a new variable named total. Think carefully about the scoping going on here. There should be one variable named total inside addTaxRate and another variable named total inside the main. Two different variables, that happen to have the same name, and that happen to hold the same value.

Eighth, print the value of total inside the main. Run and take a final screenshot. For example:

Finally, create a method named applyDiscount, similar to addTaxRate. It should be set up to take a subtotal and the percent we want to take off, so for example applyDiscount(10.00, 0.20) should return 8.0. Call it in your main and embed screenshots of you testing it for a few different values.

Optional Fun Exercise

This is completely optional, not worth extra credit or anything, just a fun warm up. I do encourage you to, as you best see fit, try basing a few Tinker journals on these optional exercises though.

This time, let's generate images with loops.

Create a new PHP web server repl using https://repl.it/new/php7. We'll use this to generate random SVG images.

Replace the index.php file contents with:

<?php
  header('Content-Type: image/svg+xml')
?>
<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
<?php

  // Shape templates we can reuse
  // The %s marks are placeholders we can fill in later
  $circle_template = '<circle
    cx="%s"
    cy="%s"
    r="%s"
    stroke="%s"
    stroke-width="2"
    fill="%s" />';
    
  $rect_template = '<rect
    x="%s"
    y="%s"
    width="%s"
    height="%s"
    stroke="%s"
    stroke-width="2"
    fill="%s" />';


  // Call printf to fill in one of the templates
  printf($circle_template, 100, 80, 100, "black", "red");
  printf($rect_template, 60, 40, 80, 80, "black", "yellow");

  // Make some random circles
  // Start at a random location
  // Then each loop, move a little in some direction
  // Then change the direction we're heading in just a tad
  $cx = rand(100, 200);
  $cy = rand(100, 200);
  $heading_x = 10;
  $heading_y = 0;
  for ($i=0; $i < 50; ++$i){
    $heading_x += rand(-3, 3);
    $heading_y += rand(-3, 3);
    $cx += $heading_x;
    $cy += $heading_y;
    printf($circle_template, $cx, $cy, 40, "transparent", "orange");
  }
  
?>
</svg>

Hit Run. You should see a red circle, a yellow square, and an orange "doodle". To re-run your code, don't press Stop then Run again. Instead, hit Repl.it's little refresh button that looks like this:

Next, look at the Manolo examples I have at the bottom of my Generative Art PDF. Try to notice the shapes in one of those drawings. Where do you see a square? a circle? a line? What colors are those shapes? Where are they placed? How big are they? Which are in the back (ie, drawn first) and which are in the front (ie, drawn last)? And how might you generate drawings like that using loops?

For example, in the very very last image in that PDF, there is a blue squiggle in the top left. That squiggle is made out of a bunch of circles drawn right on top of each other, just moved a little each time. It seems like Manolo picked a random x/y position, drew a big white circle there, then drew a smaller blue circle on top of that, then moved his x/y position a little, then drew another blue circle, and so on.

The idea here is to "decompose" the art of others into the steps and shapes that make it up, then take some ideas from that to get our own ideas going.

Then, experiment with what you can make your PHP code do! One big tip if you've never used PHP is that variable names always start with a dollar sign.

As you revise, look at your picture and check your gut: what do you like about it, what do you not like about it, and so what one small change might you make to do something better? Then check your gut and revise again. Maybe you hate the color. Maybe you hate the size. Maybe you hate the emptyness and want to add another shape. The world is your oyster.

And when you're done*, embed screenshots showing me your art!

* "When is art done? When the check clears."

Part 3/3: Open-Ended Exercise

Write a program with two methods, tallRectangle and wideRectangle. Both of these are void methods, and both of these accept a single integer parameter named size.

The tallRectangle method should print an ASCII rectangle made of * symbols. This rectangle should be 5 stars wide and size stars tall.

For example, tallRectangle(7) should print:

*****
*****
*****
*****
*****
*****
*****

Use a for loop to accomplish this method.

Similarly, the wideRectangle should print an ASCII rectangle that is 5 stars tall and size stars wide.

For example, wideRectangle(10) should print:

**********
**********
**********
**********
**********

Use multiple for loops to accomplish this method. There are multiple ways to go about this one, but if it works, it works.

In your "main," call both methods on the values 5, 10, and 15. Embed screenshots showing your final code and output. Use multiple screenshots if you need to scroll to show everything.

Submission

Complete Parts 1, 2, and 3 in a single Word/etc. document, then submit your document as a Word or PDF file (NOT a .pages file) to Blackboard.

Grading

Each Lab is worth 6/100 towards your final grade.

6/6 - Great job, maximum points! The student completes the Lab accurately and sufficiently and honestly, demonstrating the best of their ability.

3/6 - Student completes most but not all of the Lab. Or, student completes the Lab, but only to the minimal letter of the prompt, not actually applying the concepts of the unit. If you encounter problems or have questions, be sure to send me an email well before 24 hours before the due date, then continue to attempt to resolve the issue on your own while you wait for a reply.

1/6 - Student completes less than half of the Lab with sufficient work, or student leaves entire sections blank. Make sure that you are leaving yourself enough time to complete assignments, as usually students submit incomplete work because they were rushed at the last minute.

0/6 - Student does not submit on time or submits plagiarized or unacceptable work. Double check that you have submitted the right file, as usually students get zeros because they submitted a previous week's work by accident.

Tips

How Do I Make a Method?

Just for quick reference, a good place to start is watching someone else, such as these or a similar video in your language:

• #33 Python Tutorial for Beginners | Function Arguments in Python
• Methods | C# | Tutorial 12

Also continue to refer to whatever documentation has been most helpful to you so far, and reach out to me via email with any unanswered questions you have.