Announcements Announcements Reading for Wednesday(Sep 21) The - - PowerPoint PPT Presentation

Announcements Announcements

• Reading for Wednesday(Sep 21)

– The rest of the chapter 5 (not covering 5.5.2 and 5.5.3) for Wednesday

• Quiz#3 returned
• Program#2 was due today at 3:35PM

Program#2 was due today at 3:35PM

• Note: If you do not submit many programs, you will not be able to pass this

class.

• Program#3 out today
• Program#3 out today

– Explanation of program#3

Reminder: grade Reminder: grade

• 2-Midterm exams 20%
• Lab Final 10%
• Written Final

15%

• Lab activities (14 weeks) 20%

Lab activities (14 weeks) 20%

• Programs ( 8+ programs) 25%
• Homework, quizzes, and class participation 10%

T t l 100% Total 100%

Review: Queries Review: Queries

• Used to answer questions

Used to answer questions

– Return boolean value – true or false Return numeric value int or double – Return numeric value – int or double – Return String data Return other object data – Return other object data

Q

• Predicates are Queries which return

boolean values

Review: Robot Predicates Review: Robot Predicates

• canPickThing() Determine whether
• canPickThing() Determine whether

this robot is on the same intersection as a thing it can pick up thing it can pick up.

• frontIsClear() Can this robot move

forward to the next intersection safely?

Copy this to the whiteboard…

Review: RobotSE Predicates Review: RobotSE Predicates

• isFacingEast() Determine whether the

isFacingEast() Determine whether the robot is facing east.

• isFacingNorth() Determine whether
• isFacingNorth() Determine whether

the robot is facing north. i i S th() D t i h th

• isFacingSouth() Determine whether

the robot is facing south.

• isFacingWest() Determine whether the

robot is facing west.

Review: Other Robot Queries Review: Other Robot Queries

• int countThingsInBackpack() How many

g p y things are in this robot's backpack?

• int getAvenue() Which avenue is this robot
• n?
• n?
• int getStreet() Which street is this robot
• n?
• Direction getDirection() Which direction

is this robot facing?

• double getSpeed() How many milliseconds
• double getSpeed() How many milliseconds

will this robot take for the next move or turnLeft instruction? St i t St i () E ll d d l

• String toString() Every well coded class

has a toString method.

Review: IF that uses a predicate Review: IF that uses a predicate

if(this.frontIsClear()) if(this.frontIsClear()) { this.move(); this.move(); } if(!this.frontIsClear()) { this.turnLeft(); }

review: IF that uses the calling object and a di t non-predicate query

public void faceWest() { if(this.getDirection() == Direction.NORTH) { this.turnLeft(); } if(this.getDirection() == Direction.EAST) { this.turnAround(); } if(this getDirection() == Direction SOUTH) if(this.getDirection() == Direction.SOUTH) { this.turnRight(); } }

Review: IF-ELSE example Review: IF ELSE example

if(this.frontIsClear()) if(this.frontIsClear()) { this move(); this.move(); } else { this.turnLeft(); }

Review: Comparison Operators Review: Comparison Operators

• ==

==

• !=
• <
• >
• <=
• >=

>

Review: Pattern for WHILE statement

while( «test» ) while( «test» ) { t t t t t «statements to repeat» }

• braces surround the statements to repeat

and line up with while p

• the statements to repeat are indented

uniformly uniformly

Four Steps to Building a WHILE Loop Four Steps to Building a WHILE Loop

• Identify the one test that must be true

Identify the one test that must be true when the looping should stop

• Use the opposite form of the test identified
• Use the opposite form of the test identified

in step 1 as the loop «test». Withi th hil k t d

• Within the while, make progress toward

completion of the while.

• Do whatever is required before or after the

while statement is executed to ensure that we solve the given problem.

WHILE loop examples WHILE loop examples

while(this.countThingsInBackpack() != 0) { this.putThing(); } while(!this.isFacingWest()) { this.turnLeft(); }

Writing Predicates Writing Predicates

• If you are writing a predicate you do not

If you are writing a predicate, you do not always need an if statement

• The Robot class provides a predicate
• The Robot class provides a predicate

frontIsClear()

• Suppose we write a new predicate

frontIsBlocked()

Running Hurdles Running Hurdles

Problem Problem

• Write a method to make a Robot go

Write a method to make a Robot go completely around the inside of a box created by walls created by walls.

More Decision Making More Decision Making

Robots Learning to Program with Java Learning to Program with Java Byron Weber Becker

h 5 chapter 5

Chapter Objectives Chapter Objectives

• Designing while-loops

Designing while loops

• Avoiding common errors

U i t i bl

• Using temporary variables
• Nested loops
• Introducing for-loops

Common Errors Common Errors

• Endless or infinite loops are the most

Endless or infinite loops are the most common error type

• Omission errors are common on problems
• Omission errors are common on problems

like the fence post problem

Th fi t d l t iti t i ll h – The first and last positions are typically where

• mission errors occur

Attempting to fix an omission error can cause – Attempting to fix an omission error can cause an overrun error Use the loop and a half pattern – Use the loop and a half pattern

Infinite Loop Infinite Loop

• What is wrong with this loop?

What is wrong with this loop?

while(this isFacingNorth()) while(this.isFacingNorth()) { this pickThing(); this.pickThing(); this.move(); }

Another Infinite Loop Another Infinite Loop

• What is wrong with this loop?

What is wrong with this loop? int count = 10; hil ( t 0) while(count > 0) { this.putThing(); this.move(); this.move(); count++; }

Sample Problem Sample Problem

• Use a loop to move a robot along a wall

Use a loop to move a robot along a wall, ending just past the end

• The wall is of an unknown length
• The wall is of an unknown length

Writing a Predicate Writing a Predicate

• Predicates return a boolean value

Predicates return a boolean value

• Used in conditional statements

if( diti ) – if(condition) – while(condition)

• Can be negated

– if(!condition) – while(!condition)

Write a Predicate Write a Predicate

• Write a predicate that could be used to

Write a predicate that could be used to solve this problem called wallOnRight

• Recode the solution
• Recode the solution

Temporary Variables Temporary Variables

• Declare all* variables at the top of the

Declare all variables at the top of the method

• Avoid declaring variables inside control

Avoid declaring variables inside control structure bodies

• Use clear, meaningful names

Use clear, meaningful names

• Do not use one-letter* or letter-digit

variable names variable names * One exception is the counter variable that One exception is the counter variable that controls for-loops

Sample Problem Sample Problem

• Somewhere in front of your robot is an

Somewhere in front of your robot is an intersection with an unknown number of things

• Write code to count the number of things on the

g intersection

– Display the number being picked up on a label using setLabel(String)

• Repeat this (move to the next intersection with

thi t th di l i th b f things, count them, displaying the number of things being picked up) until the robot reaches a wall wall

Tracing code with variables Tracing code with variables

• What is stored in value at the end of this

What is stored in value at the end of this loop? int value = 1; int value 1; int count = 0; while(count < 5) while(count < 5)

{

l l *2 value += value*2; count++; }