8.5. Exercises: Arrays

8.5.1. Parts One And Two

OK, rookie. It’s time to train you on how to modify the shuttle’s cargo manifest. The following actions will teach you how to add, remove, modify and rearrange our records for the items stored in our hold.

  1. Create an string array called practiceFile and add the following items. Use bracket notation to update indicies 0 and 1 with items a and b to the array. Use the SetValue method to update indices 2 and 3 with items c and d.

    1. “42”

    2. “hello”

    3. “false”

    4. “-4.6”

    Code it at repl.it

    Congratulations, rookie. You can now add items to an array.

  2. Sometimes you need to update your array. Maybe the number of items is wrong, or the items need to be updated. In C#, we can change the size with the Resize method. The SetValue method and bracket notation can be used to update existing array items. Starting with the cargoHold string array {"oxygen tanks", "space suits", "parrot", "instruction manual", "20 meters", "slinky", "security blanket"}, write statements to do the following:

    1. Start by using Console.WriteLine to print all the items in the array. Use string interpolation to update the following: "The length of the array is ____". This will give us a way to check our updates.

    2. Remove the last item from the array with Resize. Print an updated length statement using a new string interpolation.

    3. Using Resize once more, extend your array by 3. Set the following items into the new indices: "1183", "meal packs", and "toothbrush". Print the new items to verify their placement.

    4. Before we move on, we need to update a few items in our array. Use bracket notation to replace "slinky" in the array with "space tether". Use SetValue to update "1183" to "keys". And update "parrot" to "flashlight" using a method of your choice.

    5. Use a Console.WriteLine to print the final array. Determine the final length and use a new string interpolation to print an updated length statement.

    Code it at repl.it

8.5.2. Parts Three And Four

Well done, cadet. Now let’s look at some finer details about array methods. We’ve got to keep our paperwork straight, so you need to know when your actions change the original records.

  1. Some methods—like Sort and Reverse—alter the original array, while others do not. Use the arrays

    string[] holdCabinet1 = new string[] {"duct tape", "gum", "3.14", "false", "6.022e23"};

    and

    string[] holdCabinet2 = new string[] {"orange drink", "nerf toys", "camera", "42", "parsnip"};

    to explore the following methods: Sort, Reverse. Refer back to the chapter if you need to review the proper syntax for any of these methods.

    1. Reverse the first array, and Sort the second. Print each array to verify your changes. What is the difference between these two methods? Do the methods alter the original arrays? How does Reverse work? What is reversed? How does Sort work? What is being sorted? How are things sorted when using Sort?

    2. Select one of the arrays. Using your array methods, update the items within the array so that they are in descending ( reverse alphabetical) order. Print the array to verify your changes.

    Code it at repl.it

    Good progress, cadet. Here are three more methods for you to examine.

  2. The Split method converts a string into an array, the Join method does the opposite, and the ToCharArray converts a string into its characters within an array.

    1. Try it! Given the string string str = "In space, no one can hear you code.", see what happens when you print str.Split() vs. str.Split('e') vs. str.Split(' ') vs. str.Split(''). What is the purpose of the parameter inside the ()? Print at least 3 indices of each Split to verify your changes.

    2. Given the array char[] arr = ['B', 'n', 'n', 5], see what happens when you print arr.Join() vs. arr.Join('a') vs. arr.Join(' ') vs. arr.Join(''). What is the purpose of the parameter inside the ()?

    3. Do Split or Join change the original string/array?

    4. The benefit, cadet, is that we can take a string with delimiters (like commas) and convert it into a modifiable array. Try it! Alphabetize these hold contents: "water,space suits,food,plasma sword,batteries", and then combine them into a new string.

    5. Strings are immutable, but arrays are mutable. So what can you do when your string has a typo? Given the string string message = "Hullo World!", use ToCharArray to fix is so that it reads Hello World!. Does ToCharArray change the original string?

    Code it at repl.it

8.5.3. Part Five: Bonus Mission

Nicely done, astronaut. Now it’s time to bring you fully up to speed.

  1. Arrays can hold many different data types, even other arrays! A multi-dimensional array is one with entries that are themselves arrays.

    1. Define and initialize the following arrays, which hold the name, chemical symbol and mass for different elements:

      1. string[] element1 = {"hydrogen", "H", "1.008"};

      2. string[] element2 = {"helium", "He", "4.003"};

      3. string[] element26 = {"iron", "Fe", "55.85"};

    2. Using bracket notation and the table array, print the mass of element1, the name for element 2 and the symbol for element26.

    3. table is an example of a 2-dimensional array. The first “level” contains the element arrays, and the second level holds the name/symbol/mass values. Experiment! Create a 3-dimensional array and print out one entry from each level in the array.

Excellent work, records keeper. Welcome aboard.