2. Chapter 5
Decisions

3. ssential uestion:
How are Boolean expressions or operators used in everyday life?

4. Terms
branch
condition
error-checking
nesting
selection
sequence

5. Making Decisions in Code
Section 5.1
Making Decisions in Code

6. Section 5.1 Learning Goal
Compare ways to control how a program runs.

7. Making Decisions in Code
Three ways to control how programs run
Sequence: program will perform the first line of code first
Selection: program can make decisions on which lines of code to execute
Repetition: loops

8. Making Decisions in Code
IF…THEN, IF…THEN…ELSE blocks
Make decisions, control actions in programs
Evaluates expressions (true or false)
Block combination provides the program’s logic
Operators category: comparison operators, also known as relational operators
Result is always true or false

9. Making Decisions in Code
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IF…THEN and IF…THEN…ELSE statements are used to make decisions and reactions in computer programming.

10. Making Decisions in Code
Condition: expression that can only be either true or false (yes or no)
Called Boolean expressions
Uses binary logic since there are only two possible outcomes
Examples
Home alarm systems
Car’s lights
Bouncing sprite off stage’s edge

11. Section 5.1 Review
When would selection program control be used over sequence program control?
Why is a condition called a Boolean expression?

12. Building Boolean Expressions
Section 5.2
Building Boolean Expressions

13. Section 5.2 Learning Goal
Apply operators to Boolean expressions.

14. Identifying Boolean Expressions
Boolean expressions make decisions
Look at the algorithm
Decision points
Branches in the program
Branch: point in code where a decision is made and a path selected based on the decision

15. Identifying Boolean Expressions
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Boolean expressions test conditions to make decisions.

16. Writing Boolean Expressions
Break complex expressions into small steps
Use operators to join conditions/outcomes
AND operator
Expression true if both conditions are true
OR operator
Expression true if either condition is true

17. Section 5.2 Review
Where are Boolean expressions found in a project’s algorithm?
Why should complex expressions be broken down into smaller steps?

18. Section 5.3
Coding Decisions

19. Section 5.3 Learning Goal
Diagram nested decision-making code statements.

20. IF…THEN Block Beginning contains the condition to test
If the condition is true,
Program executes the code contained below within the block
If the condition is false,
Program will proceed to the next block after the IF…THEN block
Use conditional operators when testing multiple conditions
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21. IF...THEN…ELSE Block
Can be used to offer alternative if condition is false
If statement is true, only first block section processed
If statement is false, only second block section processed
Programming technique for verifying correct user input
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22. Creating Nested Decisions
Nesting: technique in which one decision is contained within another decision
Second decision depends on first decision’s outcome
Makes code efficient
Processed only until problem is solved
Allows for complex response
No limit on number of statements nested

23. Creating Nested Decisions
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Nested statements are created by adding an if then or if then else block into another if then or if then else block.

24. Checking Calculations
Error-checking: programming technique for verifying correct user input
Example: user password/security question
IF…THEN…ELSE statements used to compare user’s answer to data on file

25. Section 5.3 Review
How can conditional operators be used to test multiple conditions?
Describe how nesting is similar to Russian matryoshka dolls.
Why is error-checking used in programs?