programming with logical structures - mr. harris 3/project 3 ppt...project 3: programming with...

Alice 2.0Introductory

Concepts and Techniques

Project 3

Programming with Logical Structures

Project 3: Programming with Logical StructuresProject 3: Programming with Logical Structures 2

Project Objectives

• List and describe the three major elements of

logical structure found in algorithms

• List several criteria that should be met by each

linear sequence in an algorithm

• Describe the difference between binary bypass

and binary choice branching routines

• Describe the difference between a pretest loop

and a posttest loop

• List and describe the four major parts of a count-

controlled loop

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Project Objectives

• List and describe the six logical comparison operations

used in computer programming

• List and describe the three major operations in Boolean

logic

• Create methods in Alice that implement each of the

following

– a binary bypass

– a binary choice

– a count-controlled loop

– a sentinel loop that is not count controlled

• Create a compound Boolean expression in an Alice

looping or branching instruction



Project 3: Programming with Logical Structures

Project Overview

• Project 1 (skaterHello.a2w)

• Project 2 (skaterRoutine.a2w)

• Project 3 (skaterLogic.a2w)

– Modify the skaterRoutine.a2w

– Use logical structures to control the behavior of the skater

– Change the documentation

– Add a flag pole to the world




Creating a New World

from an Existing World – pp. 134-137

• Start Alice

• Open skaterRoutine.a2w

• Update documentation

– Program name

– Date

– Program description

• Save as skaterLogic.a2w




The Logical Structure of Algorithms

• Algorithm – a step-by-step process

• OOP – each method is an algorithm

• Corrado Bohm and Giuseppe Jacopini (Italian

mathematicians)

– 1960s

– Showed that all algorithms are composed of three

elements of logical structure

• Selection sequences – branching routines

• Repetition sequences – loops

• Linear sequences – in order




Flowcharts

• Graphical depiction of an

algorithm using symbols

• Flowcharting template




Linear Sequences

• All the previous Alice methods written have been linear sequences –executed one after the other

• Steps executed one after another with no looping or decisions

• Criteria to meet

– Clear starting and ending points

– Entry and exit conditions clearly stated

– Sequence of instructions are complete

– Sequence of instructions are in the proper order

– Each instruction in sequence needs to be correct




Selection Sequences – Branching

• Occurs whenever the flow of instructions splits into separate paths

• Must have a condition to determine the path to follow

• Binary branching

– Flow of logic splits into two possible paths

– True-or-false condition

• Multiple branching

– Flow of logic divides into more than two paths

– Single condition with many possible values

BinaryMultiple




Binary Branching

• Binary bypass

– Instruction is either executed or bypassed

– It is possible that nothing will happen

• Binary choice

– One of two instructions, but not both, is executed

– One of the two instructions will definitely be executed

• If/Else instruction tile (bottom of Editor area)

Bypass Choice




Binary Bypass – pp. 141-144

• Built-in functions (World object)

– Day of year – used to return the day of the year from the computer’s system clock

– a==b – function used to see if the day of the year is equal to 1




Binary Choice – pp. 144-146

• AM built-in function (World object)

– Returns a value of true if the time on the system clock is before 12:00 PM

– Returns a value of false if the time on the system clock is 12:00 PM or after




Multiple Branching

• Questions with many

possible answers

• Alice does not have

an instruction for

multiple branching

Visual Basic Statement




Multiple Branching

• Same results

can be achieved

by asking a

series of binary

questions

(If/Else

instructions)

Series of Binary

Branching Routines

Series of Nested

If/Else Instructions




Repetition Sequences - Looping

• Formed whenever a branch in an algorithm leads

back to a previous instruction

• While

– True – block of code is executed

– False – block of code is ignored




Adding a Flagpole to the skaterLogic

World – pp. 150-152

• ADD OBJECTS button – Objects/Flagpole

• Drag flagpole to back of world

• Resize flagpole – (right-click and methods)




Capturing the iceSkater in a New

Pose – pp. 153-156

• Object tree – iceSkater tile

– Select left lowerLeg

– Methods (right-click) – change

position of left lowerLeg

• Properties tab

– Capture pose

– Name it – leftFootUp




Creating the glideStep method – pp.

156-160

• iceSkater will push and glide until she is within

three meters of the flagpole – loop

• iceSkater will move one meter while pushing

with her left foot

• iceSkater will glide two meters on her right foot

with her left foot raised behind her (left FootUp

position)




Creating the GlideStep Method – pp.

156-160




Adding a While Loop to the Closing

Method – pp. 160-163

• iceSkater

– Turns to face flagpole

– Continues to execute glide steps while she is more than three meters away from the flagpole

– Loop will stop when she is <= three meters from the flagpole

• While instruction tile (bottom of Editor area)

• a > b function (World object)




Pretest and Posttest Loops

• Pretest loop– Test occurs before the body of the loop

– Body of loop does not have to execute

– While

• Posttest loop– Test occurs after the body of the loop

– Body of loop will execute at least once

– Alice does not have an instruction for a posttest loop

PretestPosttest




Count-Controlled and Sentinel Loops

• Sentinel loop

– Marker or condition that tells the computer when to

stop executing a loop

– Every loop is a sentinel loop (no infinite loops)

• Count-controlled loop

– Sentinel loop in which the sentinel is a counter that

is not allowed to go beyond a certain value




Count-Controlled Loops

• Counter

– Variable that is updated each time the program runs through the loop

– Must have an initial value, a final value, an increment

• Four parts

– Initialization – sets the first value of the control variable

– Test – checks the control variable to see if the loop should be executed

– Processing – repeats the instructions in the body of the loop

– Update – changes the value of the control variable each time the loop is executed




Loop Instruction

• Simple version – shows only the number of times the loop

is to be repeated

• Complicated version – shows the control variable, named

index, initial value, final value, increment value

• Loop instruction tile (bottom of Editor area)

SimpleComplicated




Adding a Count-Controlled Loop to

the Routine Method – pp. 166-167

• ice-Skater will repeat the figure eight three times




Comparison Operators

• Operators that allow for a comparison of two

values




Boolean Logic

• George Boole (mathematician)

– 1854

– Boolean logic – only values used are true and false

• Three basic operations

– AND

– OR

– NOT




Adding a Compound Boolean Expression

to the Opening Method – pp. 169-173

• December 22 – shortest day of the year




Testing the skaterLogic Alice 2.0

World – p. 173

• Play button

• Methods should be called in order




Project Summary

• List and describe the three major elements of

logical structure found in algorithms

• List several criteria that should be met by each

linear sequence in an algorithm

• Describe the difference between binary bypass

and binary choice branching routines

• Describe the difference between a pretest loop

and a posttest loop

• List and describe the four major parts of a count-

controlled loop




Project Summary

• List and describe the six logical comparison operations

used in computer programming

• List and describe the three major operations in Boolean

logic

• Create methods in Alice that implement each of the

following:

– a binary bypass

– a binary choice

– a count-controlled loop

– a sentinel loop that is not count controlled

• Create a compound Boolean expression in an Alice

looping or branching instruction



programming with logical structures - mr. harris 3/project 3 ppt...project 3: programming with...

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