Lesson 15: Conditionals

Display: Display the following questions on the board and ask students to answer them.

The last two prompts ask students to react to information that may change as they are answering the questions. In order to drive this point home, consider moving from the front of the room and back, as well as alternately tapping and not tapping a pencil, so that students realize that their answers may change according to when they are answering each question.

1. If your last name has more than five letters, draw a square on your paper.
2. If your last name less than seven letters, draw a circle.
3. If you are wearing anything green, add 3 + 2.
4. If the teacher is tapping their pencil, draw an 'X'.
5. If the teacher is in the front of the room, fold your paper in half.

Prompt: When we program, we give the computer instructions on what to do. How are the instructions you just followed different from the instructions that we have been giving in Game Lab?

Think-Pair-Share: After students have had a chance to write down their answers, allow them to talk to a partner before sharing out as a class.

Discussion Goal: This discussion should prepare students to investigate programs that react to changing conditions. Students should realize that there is no "one way" that these questions will be answered, and that the answers will change according to changing conditions.

These instructions were a little different because we first had to decide whether something was true or not before we knew what we should do. In programming, instructions that depend on whether or not something is true are called conditionals, and the thing that is checked is called the condition. Conditionals are especially useful when we want the program to react to situations that change while the program is running.

Key Vocabulary:

• Condition - Something a program checks to see whether it is true before deciding whether to take an action.
• Conditionals - Statements that only run under certain conditions.

Question of the Day: How can programs react to changes as they are running?

Transition: Send students to Code Studio.

Guide to Programming Levels: Additional guidance for programming levels is provided in the CSD Guide to Programming Levels. This document includes strategies and best-practices for facilitating programming levels with students.

Video: Show students the Boolean Expressions video in the slides.

To encourage active engagement and reflection, use one or more of the strategies discussed in the Guide to Curriculum Videos.

Questions to Consider with Video:

• What is a Boolean expression?
• What’s an expression that would evaluate to true?
• What’s an expression that would evaluate to false?

Discussion Goal:

• What is a Boolean expression?
  • Boolean Expression - in programming, an expression that evaluates to True or False.
  • Students should be able to explain that a Boolean expression is something that is either true or false, similar to a yes or no question.
  • The more formal way to say this is that Boolean expressions evaluate to either true or false. That means that when the computer processes a Boolean expression, it checks to see whether the expression describes a situation that is true or false, and then uses the value of either true or false wherever the expression is found.
• What’s an expression that would evaluate to true?
  • Some examples of Boolean expressions that evaluate to true are 3 > 1 and 4 <= 7, but press students to think of expressions that might be better represented by variables, such as studentAge < 70 or sizeOfClass > 2.
• What’s an expression that would evaluate to false?
  • Some examples of Boolean expressions that evaluate to false are 4 == 7, schoolName == "Hogwarts", and currentYear < 1000.

Video: Show students the Conditional Statements video in the slides.

Question to Consider with Video:

• When would you want to use an if statement?

Discussion Goal: The broad point of this question is that programmers use if statements when they want the program to run differently in response to different situations. Encourage students to think of particular situations in which this would be the case. For example, they might want their characters to move faster when a "bonus" is in effect, or maybe they want more enemies to appear when the player reaches a certain level. Maybe they want the program to react in some way if a user presses a key or clicks the mouse, or they want a character to change animations if it touches a particular item.

Formative Assessment: This level can be used as a formative assessment. A rubric is provided in the level, and written feedback can be given to students. Click here to learn more about giving feedback to students.

Question of the Day: How can programs react to changes as they are running?

Key Vocabulary:

• Condition - Something a program checks to see whether it is true before deciding to take an action.
• Conditionals - Statements that only run under certain conditions.
• Boolean Expression - In programming, an expression that evaluates to True or False.

Prompt: Now that you know how conditionals work, where you do think that they are used in games or other programs and apps that you already use?

Discuss: Have students share responses.

Discussion Goal: This discussion should get students thinking about how conditionals are used in games they have already seen, and help them connect those ideas to how they might want to use conditionals in their own programs. Student responses might include:

• If my username and password are correct, log me into Facebook
• If Pacman has collected all the balls, start the next level
• If my keyboard or mouse hasn't moved in 10 minutes, turn on the screensaver