Lesson 2: Operators and Expressions

Computer science impacts all aspects of our society in different ways.

In many cases, computer science has significantly changed how things are done and improved how people and businesses operate.

Do This: Share the example of computer science in business.

Do This: Direct students to write down ideas and thoughts in response to the prompt on a sticky note or scrap piece of paper.

Students participate in a Give One, Get One activity during the wrap up to share their ideas with their peers.

In the previous lesson, we learned how to create primitive variables and change their values. We can also use these variables in expressions.

Do This: Review the lesson objectives.

Do This: Introduce arithmetic operators.

Briefly explain the functionality of each arithmetic operator – addition, subtraction, multiplication, division, and modulus ( % ). You do not need to spend time explaining how each of these functions here since these are explored throughout the lesson.

Discuss: Use the Retrieve-Pair-Share strategy to discuss the prompts.

• Where have you seen operators like these before?
• How did you use these operators?

Discussion Goal: Students recall arithmetic operators used in math class to perform calculations.

Do This: Direct students to Level 1 on Code Studio to predict the program's outcome, then run the program to compare their predictions to the actual outcome.

Discuss: Click through the animated slide to display the prompts.

• What do you notice about the code in this program?
• What do you wonder about the code in this program?

Discussion Goal: Students notice that dividing two int values results in a whole number. Students may wonder why the decimal portion is lost.

Do This: Click through the animated slide to define operand and expression.

Do This: Click through the animated slide to explain how the value and type of the operand impact how the expression is evaluated.

Do This: Click through the animated slides to demonstrate evaluating expressions and storing the value in a variable.

• When processing assignment expressions, evaluate the statement on the right then store the value in the variable on the left.
• When evaluating multiple expression statements in a row, the updated value that has been stored in the variable is the value that is used in future expressions.

Do This: Click through the animated slide to demonstrate evaluating dividing two int values and define truncate.

Do This: Click through the animated slide to demonstrate dividing an int and a double by 0 and define ArithmeticException.

Do This: Click through the animated slide to demonstrate evaluating expressions using the mod ( % ) operator.

Discuss: Use the Hold That Thought strategy to discuss the prompt.

• When would the mod operator be useful?

Discussion Goal: Students suggest using the mod operator to determine if a number is a multiple of another number. Students note that the mod operator could also determine if a number is even or odd.

Group: Place students in pairs.

Do This: Direct students to Level 2 on Code Studio to investigate the program with a partner. Students make the changes to the program as prompted.

Do This: Explain the order of operations:

• Introduce the order of operations
• Respond to the self-check question

Do This: Click through the animated slide to define compound assignment operator and demonstrate the examples.

The type of the operands impacts how an operator behaves. We used concatenation in the previous unit to combine values with a String to print information about the state of a Painter object.

Do This: Click through the animated slide to review concatenation and demonstrate using operators with a String.

Point out the space inside the quotation marks with the text "Hello". Note that not including the space would display "HelloWorld" instead of "Hello World". Java prints exactly what is given inside quotation marks, so spaces should be included when needed to ensure the proper appearance of printed text.

At the beginning of this lesson, we heard about how computer science influences businesses. Let's revisit the ideas and thoughts you had and share these with your peers. It's time to…

Do This: Play the music clip to cue the Give One, Get One activity and direct students to participate in a Give One, Get One.

Discuss: Click through the animated slide to display the prompts.

• What did you learn from each other?
• How do these ideas and thoughts contribute to your identity as a software engineer?

Discussion Goal: Students share their thoughts and ideas about computer science in business. Students identify aspects that relate or contribute to their identity as software engineers and may wonder about potential careers.

Do This: Review the concepts covered in this lesson.

Display: Key Vocabulary

Check For Understanding Question(s) and solutions can be found in each lesson on Code Studio. These questions can be used for an exit ticket.

To assign questions from the AP Classroom Question Bank that align with this lesson, create a custom quiz in AP Classroom by searching the Question Bank for the Essential Knowledge statements listed at the top of this lesson plan. You can find instructions and video demonstrations to do this on AP Central.

The following Topic Questions in AP Classroom can be assigned as a formative assessment for this lesson:

• Topic Questions 1.3
• Topic Questions 1.4

Note: Some Learning Objectives and Essential Knowledge statements in the suggested Topic Questions are covered in later units.