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Programming Structure CS 104 9/7/11
Programming Structure
CS 104
9/7/11
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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
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Unstructured Code: Spaghetti Code
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory
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Three Basic Structures Three basic structures in programming
Sequence structure Decision structure Loop structure
The design dictates which structures are required
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Sequence Structure
Sequence: one action occurs after another
Most basic structure
Sequence Structure ExampleWake up
Turn off alarm
Eat breakfast
Brush teeth
Shower
Get dressed
Pack bookbag
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Draw a square in Scratch
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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
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 existsif car needs gas then
get gas
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Decision Structure
It’s possible that only one process existsif car needs gas then
get gas
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Decision Structure
Decision Statement Example
if weather = raining then
wear rain boots
else
wear sandals
end if
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Decision Statement Example
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Football score calculatortouchdown = 6extra point = 1field goal = 3safety = 2
Modify square program to ask the user if he/she wants to make another square
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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
Loop Structure Example
while quarter < 5
quarter = quarter + 1
end while
Loop the square drawing program
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Three Basic Structures Sequence of all three structures
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory
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Three Basic Structures Nesting structures can be necessary
Sequence within a Decision statement
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory
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Why Use Structure? Increases readability Allows for multiple programmers to work on the
same program (modularity) Help identify errors more quickly
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Flowchart and Pseudocode of Structured College Admission Program
Ferrell, Joyce. Programming Logic and Design, Third Edition Introductory
Notice how much easier this is to read than the spaghetti code version
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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
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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
=)
