1. Programming Structure
CS 104
9/7/11

2. Agenda Go over Quiz Quiz #2 9/14
Discuss Assignment #1 due today (11:59pm)
Discuss Assignment #2 due 9/21 (11:59pm)
Finish slides from Wednesday
Introduction to programming logic and BYOB Scratch

3. Unstructured Code: Spaghetti Code
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory

4. Three Basic Structures
Three basic structures in programming
Sequence structure
Decision structure
Loop structure
The design dictates which structures are required

5. Sequence Structure Sequence: one action occurs after another
Most basic structure

6. Sequence Structure Example
Wake up
Turn off alarm
Eat breakfast
Brush teeth
Shower
Get dressed
Pack bookbag
Draw a square in Scratch

7. Decision Structure
Just as the name implies, the decision structure requires making a decision
A true/false question is asked, and the program chooses one of two paths depending on whether the answer is true or false

8. Decision Structure
Also known as an if-statement or an if-then-statement
if condition is true then
do processA
else
do processB
It’s possible that only one process exists
if car needs gas then
get gas

9. Decision Structure It’s possible that only one process exists
if car needs gas then
get gas

10. Decision Statement Example
if weather = raining then wear rain boots else wear sandals end if

11. Decision Statement Example
Football score calculator
touchdown = 6
extra point = 1
field goal = 3
safety = 2
Modify square program to ask the user if he/she wants to make another square

12. Looping Also referred to as Iteration or Repetition
A question is asked, if the answer is true, the specified action is performed, and the question is asked again
Different types of loops
Do Until – do the action until the question is true
Do While – do the action while the question is true
For – repeats a specific number of times

13. Loop Structure Example
while quarter < 5
quarter = quarter + 1
end while
Loop the square drawing program

14. Three Basic Structures
Sequence of all three structures
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory

15. Three Basic Structures
Nesting structures can be necessary
Sequence within a Decision statement
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory

16. Why Use Structure? Increases readability
Allows for multiple programmers to work on the same program (modularity)
Help identify errors more quickly

17. Flowchart and Pseudocode of Structured College Admission Program
Notice how much easier this is to read than the spaghetti code version
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory

18. Pseudocode for Rock, Paper, Scissors
Sequence, Decision, and Looping structures can be used to solve almost any problem
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory

19. Summary
Spaghetti code is unorganized making it difficult to read and maintain
Three types of structures: sequence, decision, loop
Assignment #2 due 9/21
Quiz #2 9/14
Install BYOB Scratch and start trying it out =)