Programming Structure CS 104 9/7/11

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 =)