unit 6 assignment array statistics

# Unit 6: Array

# lesson 1: one-dimensional arrays, # lesson 2: traversing an array, # lesson 3: arrays of strings, # lesson 4: algorithms on arrays, # lesson 5: the enhanced for loop, # assignment 6: array statistics.

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Source code for the 2022-23 AP Computer Science A course on Project Stem.

ricky8k/APCSA-ProjectStem

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Source code for the 2022-23 AP Computer Science A course on Project Stem. Browse the source code »

This repository contains the source code to various problems on Project Stem. Organized by unit, you will find the necessary activity files to be compiled by the Java environment, as well as runner files provided by Project Stem to test execution (when available).

The provided source code is intended to work with the 2023 AP CS A course. These solutions may grow out-of-date as new changes are made to the course every year.

The user-friendly website front-end found here is built using Retype .

Table of Contents

• Unit 1: Primitive Types
• Unit 2: Using Objects
• Unit 3: Boolean Expressions and If Statements
• Unit 4: Iteration
• Unit 5: Writing Classes
• Unit 6: Array
• Unit 7: ArrayList
• Unit 8: 2D Array
• Unit 9: Inheritance
• Unit 10: Recursion

📝 Contributing

Notice a typo or error? Feel free to create an issue !

Please note that support will not be provided for code that does not work in newer lessons. As such, the source code will not be updated to reflect newer curricula.

This repository is licensed under GPL 3.0 .

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Goldie's AP® Computer Science A Coding Projects for Unit 6: Arrays

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Description

AP® Computer Science A (AP® CSA)

Coding Projects with Arrays

The material covered in these projects aligns with Unit 6 of the AP® CSA CED. These projects ask students to code in the Java programming language.

All projects come with both the editable WORD document, the PDF version, as well as an answer key. You will have the ability to change directions or edit anything to fit your own classroom needs.

Daycare Statistics Project – Students are taken through the steps to import a data file into their program, put the contents into an array, and then work with the common array algorithms.

Multiplication Facts Practice Project – Students will use arrays to make a program that helps the user practice their multiplication facts.

Sum of Two Dice Simulator Project – Statistics and Computer Science cross over in this program where students will simulate rolling a die a certain number of times and use arrays to store their answers.

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Interested in more AP® CSA material? You can find these Unit 6 coding projects in the following resources:

Goldie's AP® Computer Science A UNIT 6 PLANS - Arrays

Goldie's FULL CURRICULUM for AP® Computer Science A

Explore my other Java Coding Projects resources:

Unit 1: Primitive Types Coding Projects

Unit 2: Using Objects Coding Projects

Unit 3: if Statements Coding Projects

Unit 4: Iteration Coding Projects

Unit 5: Writing Classes Coding Projects

Unit 6: Arrays Coding Projects

Unit 7: ArrayLists Coding Projects

Unit 8: 2D Arrays Coding Projects

Unit 9: Inheritance Coding Projects

Unit 10: Recursion Coding Projects

Goldie's AP® Computer Science A Coding Projects Bundle

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Unit 6 Overview: Array

3 min read • january 8, 2023

Athena_Codes

The Big Takeaway Of This Unit

Unit overview, exam weighting.

• 10-15% of the test
• Roughly  4 to 6  multiple-choice questions
• A possible topic of  FRQ #3 , which may test your ability to  make arrays and array algorithms .

Enduring Understanding

In this unit, we will start learning about  data structures , which are structures that store multiple pieces of data. You will learn about three of them in this course: 1-D Arrays in this unit, ArrayLists in Unit 7, and 2-D Arrays in Unit 8.  Arrays store one type of data, whether that be a primitive data type or a reference data type , and they are of fixed size . When used for loops , we can do many things with arrays and build algorithms with them, as well.

Building Computational Thinking

In this unit, you will learn three things that are important for larger programs: how to create an array, how to  traverse (going through all the elements) an array, and how to manipulate the elements in an array. One of the common mistakes that you may make at first is an ArrayIndexOutOfBoundsException , which occurs when you try to access an element where none exists, but with some practice, you will be flawless with arrays !

Main Ideas for this Unit

• Initializing Arrays

Accessing Elements in Arrays

Traversing Arrays

• Array Algorithms

6.1: Array Creation and Access

Introduction to arrays.

Arrays  are used to store one type of data, whether it is a primitive or reference data type . Arrays themselves are reference types. They are best thought of as a list of items with a fixed size , as arrays have a set size that cannot be changed (don’t confuse this with ArrayLists which can also be thought of as a list). Arrays are denoted by braces ({}), with items separated by commas such as the following:

Before we can use arrays , we need to have an import statement, which is

Making Arrays

There are two ways to make arrays : using a constructor and using a pre-initialized array.

Constructor

As with other reference types, we can initialize arrays using a constructor . However, the constructor is slightly different from the constructors from Unit 5:

The items in the array are initialized differently depending on the data type. Integers are initialized to 0, doubles are initialized to 0.0, booleans are initialized to false, and all reference types are initialized to null. We will talk about filling constructed lists in the next topic when we discuss traversing arrays .

Pre-initialized Arrays

We can also set an array to a pre-initialized array, similar to how we initialize strings. Here, we will initialize an array of 10 integers as follows:

We access elements in arrays using bracket notation as follows:  arrayName[index] . The most important thing to know is that Java is a  zero-indexed language ,  so the first item has index 0, and not 1.

Before we talk about the index of the last item, we need to discuss how to find the array length. The array length is actually an instance variable specific to that particular array denoted as  arrayName.length  (not to be confused with length() for Strings). Note that this is not a method, so there are no parentheses. Thus, the last item in the array can be accessed by using  arrayName.length - 1 . Do not confuse this with the constructor in which we use  arrayName.length in brackets. If we use an index outside the allowed range, we will get an  ArrayIndexOutOfBoundsException .

Here is a question: how do we access the even numbers in arrayOne from above?

2 = arrayOne[1]

4 = arrayOne[3]

6 = arrayOne[5]

8 = arrayOne[7]

10 = arrayOne[9]

Key Terms to Review ( 13 )

ArrayIndexOutOfBoundsException

arrayName.length

arrayName[index]

Primitive data type

Reference Data Type

Zero-indexed language

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• 6.1 Array Creation and Access
• 6.2 Traversing Arrays with For Loops
• 6.3 Enhanced For-Loop (For-Each) for Arrays
• 6.4 Array Algorithms (FRQs)
• 6.4.1 Free Response - Horse Barn A
• 6.4.2 Free Response - Horse Barn B
• 6.4.3 Free Response - Self Divisor B
• 6.4.4 Free Response - Sound A
• 6.4.5 Free Response - Sound B
• 6.4.6 Free Response - Number Cube A
• 6.4.7 Free Response - Number Cube B
• 6.5 Unit 6 Summary
• 6.6 Mixed Up Code Practice
• 6.7 Toggle Mixed Up or Write Code Practice
• 6.8 Code Practice with Arrays
• 6.9 Multiple-Choice Exercises
• 6.10 Practice Exam for Arrays
• 6.11 More Code Practice with Arrays
• 6.4.7. Free Response - Number Cube B" data-toggle="tooltip">
• 6.6. Mixed Up Code Practice' data-toggle="tooltip" >

6.5. Unit 6 Summary ¶

In this chapter you learned about Arrays . An array is consecutive storage for multiple items of the same type like the top five scores in a game. You learned how to declare arrays, create them, and access array elements. Array elements are accessed using an index. The first element in an array is at index 0.

Figure 1: Two 5 element arrays with their values set to the default values for integer and object arrays. ¶

6.5.1. Concept Summary ¶

Array - An array can hold many items (elements) of the same type. You can access an item (element) at an index and set an item (element) at an index.

Array Declaration - To declare an array specify the type of elements that will be stored in the array, then ( [] ) to show that it is an array of that type, then at least one space, and then a name for the array. Examples: int[] highScores; String[] names;

Array Creation - To create an array type the name and an equals sign then use the new keyword, followed by a space, then the type, and then in square brackets the size of the array (the number of elements it can hold). Example: names = new String[5];

Array Index - You can access and set values in an array using an index. The first element in an array called arr is at index 0 arr[0] . The last element in an array is at the length minus one - arr[arr.length - 1] .

Array Initialization - You can also initialize (set) the values in the array when you create it. In this case you don’t need to specify the size of the array, it will be determined from the number of values that you specify. Example: int[] highScores = {99,98,98,88,68};

Array Length - The length of an array is the number of elements it can hold. Use the public length field to get the length of the array. Example: given int[] scores = {1,2,2,1,3,1}; , scores.length equals 6.

Element Reference - A specific element can be referenced by using the name of the array and the element’s index in square brackets. Example: scores[3] will return the 4th element (since index starts at 0, not 1). To reference the last element in an array, use array[array.length - 1]

For-each Loop - Used to loop through all elements of an array. Each time through the loop the loop variable will be the next element in the array starting with the element at index 0, then index 1, then index 2, etc.

Out of Bounds Exception - An error that means that you tried to access an element of the array that doesn’t exist maybe by doing arr[arr.length] . The first valid indices is 0 and the last is the length minus one.

6.5.2. Java Keyword Summary ¶

for - starts both a general for loop and a for-each loop. The syntax for a for each loop is for (type variable : array) . Each time through the loop the variable will take on the next value in the array. The first time through the loop it will hold the value at index 0, then the value at index 1, then the value at index 2, etc.

static - used to create a class method, which is a method that can be called using the class name like Math.abs(-3) .

6.5.3. Vocabulary Practice ¶

• The index of the last element
• The number of elements in the array
• The index of the first element
• The index of the second element
• Declare an integer array named nums
• int[] nums;
• Declare and create a String array named list1 that can hold 3 elements
• String[] list1 = new String[3];
• Initialize an array of integers named nums to contain the first 3 whole numbers
• int[] nums = {1,2,3};
• Initialize a String array named list1 to contain the first 3 letters of the alphabet as separate strings
• String[] list1 = {"a", "b", "c"};

For more practice, see this Quizlet .

6.5.4. Common Mistakes ¶

forgetting to create the array - only declaring it ( int[ ] nums; ) using 1 as the first index not 0 using array.length as the last valid index in an array, not array.length - 1 . using array.length() instead of array.length (not penalized on the free response) using array.get(0) instead of array[0] (not penalized on the free response) going out of bounds when looping through an array (using index <= array.length ). You will get an ArrayIndexOutOfBoundsException . jumping out an loop too early by using one or more return statements before every value has been processed.