Lab: Arrays

Overview

In this lab, we'll practice working with arrays. Arrays are fundamental to computer science, especially when it comes to formulating various algorithms. We've already learned a bit about arrays through the String data type. In many ways, a character string reveals the secrets of arrays:

• each element of a string is a common type (Char)
• we can use indexing to find any given character, e.g. s(i) gives us the character at position i.
• we know that the string has a finite length, e.g. s.length.

So you've already learned these concepts. But practice is useful creating and manipulating arrays with different kinds of data.

Goals

In this lab, we're going to practice:

• creating arrays that hold numerical data
• populating an array with data
• using the tools of loops and decisions to do something interesting with the data
• printing the data
• learning how to return values from functions to pass unit tests

Tasks

• Sign into GitHub with your user ID.

• Use GitHub to fork your own copy of this lab. This is achieved by visiting https://github.com/LoyolaChicagoBooks/introcs-scala-arrays and pressing the Fork button you see in the upper right corner.

  git clone https://github.com/YourGitHubUsername/introcs-scala-arrays.git
  

• Make modifications to arrays/arrays.scala. You might want to copy the file arrays.scala to a backup name just in case you need to start over with the lab assignment (e.g. `cp arrays.scala arrays.scala-orig).

• Complete the body of each function using the description and/or provided hints.

• Recall that you can declare an array in two ways:

  val myArray1 = Array[Int](10)
  val myArray2 = Array[Int](7, 7, 3, 5, 5, 5, 1, 2, 1, 2)

• Scala can also infer the type of an array, as long as you have taken care to ensure each argument has the same type.

  val myArray3 = Array(7, 7, 3, 5, 5, 5, 1, 2, 1, 2)

Hints

• Your job is to modify each of the functions in arrays.scala. We recommend that you do these modifications one at a time.

• Run sbt test to compile and test all of the functiosn in arrays.scala. You will likely see a lot of failed tests (in red text) and very few passed tests (in green). As you write each of the functions, more and more tests will start to pass (turn green), which is the point of this lab.

• The first method has already been implemented as an example:

  def arraySize(a : Array[Int]) : Int = {
    a.length
  }

  The "requirement" of this function was to get the size of an array of Int (Array[Int]). When you run sbt test, you will notice that this test "passes" because the actual length of the array was returned.

• You can also look at the file arrays_tests.scala to see how each of the tests are being done. We'll go over this when running the lab, but you may find that you can learn a lot about how to implement a method by looking at the test code. Our test code makes use of some advanced Scala features not yet covered in class.