1. Lesson 5 - Decision Structure By: Dan Lunney
Computer Programming 12
Lesson 5 - Decision Structure
By: Dan Lunney

2. If /Then / Else statement
Decision logic structure is used to make a decision that has 2 outcomes: true or false
We test which it is by using the if/then/else statement
IF <condition> THEN <True set of instructions> ELSE <False set of instructions>

3. If/Then/Else Flowchart
Start
IF <condition (s)>
TRUE
FALSE
Instructions if conditions are false
Instructions if conditions are true
Exit

4. Nested If/Then/Else
We can have a second if/then/else statement as the set of instructions for the True and/or False condition of another if/the/else statement
This is called a nested if/then/else

5. Nested If/Then/Else Flowchart
Start
FALSE
TRUE if
FALSE
TRUE if
Instructions
Instructions
Instructions

6. Three Types of Logic Straight-through (no else part) Positive Logic
Negative Logic

7. Straight-Through Logic
All if statements are executed sequentially
There is no ELSE branch to be executed
This type of logic is the least efficient because we need to write a code statement for every possible decision

8. Straight Logic FlowchartIF F T IF F T IF F

9. Positive Logic Most common type as this is how we think
Continues to processing decisions until a decision is true then it stops executing

10. Positive Logic Flowchart
Start
TRUE
FALSE if
TRUE
FALSE if
Instructions
Instructions
Instructions
Exit

11. Negative Logic Works the opposite as Positive Logic
Continues to process decisions until a decision is false then it stops executing

12. Negative Logic Flowchart
Start
FALSE
TRUE if
FALSE
TRUE if
Instructions
Instructions
Instructions

13. Sample Problem – Lesson 5
What would the flowcharts and algorithms of the following problem look like in straight logic, positive logic, and negative logic?
People pay $7 for movies if they are under 16, $10 if they are between 16 and 65, and they pay $5 if they are greater than 65.
See sample problem sheet