Intro to Programming & Algorithm Design Decisions Decisions Decisions 1 Copyright 2003 by Janson...

Intro to Programming & Algorithm Design

Decisions Decisions Decisions

1Copyright 2003 by Janson Industries

This presentation can be viewed on line in a file named: ch04.IntrotoProg.ppt

Assg

Copyright 2014 by Janson Industries

Objectives Explain

Boolean expressions

Comparison operators

IF/THEN/ELSE logic

AND and OR logic

Nested IFs

Case structure

2


Decision Structure Up till now all instructions in a

module executed in sequence i.e. Statements executed in order from

top to bottom

Decision structures allow programmer to define the specific condition(s) when a statement should be executed

Conditions specified as Boolean expressions

3


Boolean Expression Results in a value of true or false

Most basic consists of

Constant Value or Variable Comparison Operator Constant Value or Variable

Examples gender = "F" hoursWorked > 40

4


Boolean Expression Values in expression can be a

variables or constants In both examples, the first value

was a variable and the second was a constant

But it doesn't have to be that way

Most languages support the following comparison operations Equal, Not Equal Greater Than, Less Than

5


Boolean Expression In addition you can combine

equal, greater than, and less than to form Greater Than or Equal Less Than or Equal

Different languages support comparison operations with different commands .equals EQ equal 6


Boolean Expression Most support the algebraic symbols

> - greater than < - less than >= - greater than or equal to <= - less than or equal to

Equal and Not Equal are a little tricky A = 10 in many languages, assigns the

value 10 to the variable A A == 10 compares variable A to the

constant value 10 7


Boolean Expression Not Equal often expressed as

<> - not equal

However Java, and the various versions of C use != Exclamation point means not

Examples state != "FL" isPrint = !true !(salary > 75000)

8


Boolean Expression Negative logic can be confusing

Try not to use

For instance, instead of if (!(salary > 75000))

Use if (salary <= 75000)

Often, in programming languages, the Boolean expression is enclosed in ()

9


Boolean Expression However sometimes the non-

negative logic is not viable

For instance, the alternative to state != "FL"

Would be 49 conditions, which would be much more code and therefore Less efficient More likely to have errors

10


Boolean Expression Can perform same selection

with different operators

11

If (price > limit) Then finalCost = price * luxuryTax Else

finalCost = price * salesTax Endif

If (price <= limit) Then finalCost = price * salesTax Else

finalCost = price * luxuryTax Endif


Boolean Expression Which one is better?

The one that is more efficient The one that causes the fewer number

of statements to be executed

How determine? Need to know business/data

Are more than 50% of the prices over or under the limit?

• If over limit, check price > limit first• If under limit, check price <= limit first

12


Boolean Expression Gotcha Must compare values of the same type

Bad expressions: totalCost == "Joe Smith"

TotalCost is a numeric variable

gender > 10 Gender is a string variable

10 == "A" Comparing a number to a string

13


Decision Structure In pseudocode, use the word If followed by

a Boolean condition in parenthesis

Statements to be executed if true follow Then and are indented

14

If (month == 1) Then

Display “Jan”

End If

If (month == 2) Then

Display “Feb”

End If


Boolean Expression In flow charts, put into diamond

symbol (selection)

Two logic paths out of diamond True

False

15

month== 1

Display “Jan”

True

False

month== 2

Display “Feb”

True

False


Java if Statement

16

if (month == 1) {System.out.println(“Jan”);

}if (month == 2) {

System.out.println(“Feb”);}

Syntax of an if/else statement if(boolean expression) { statements to be executed if true }


Java if Statement

17

String gender; : :if (gender.equals(“f”)) {

System.out.println(“Female”);}if (gender.equals(“m”)) {

System.out.println(“Male”);}

When comparing a String variable must use .equals


Dual Alternative Decision Can specify what should happen if

condition is false

In pseudocode, use the word Else and indent statements to be executed if false

18

If (gender == “F”) Then

Display “Female”

Else

Display “Male”

End If


Dual Alternative Decision Have false leg come out the left

side of the diamond

19

gender == “F"

TrueFalse

Display “Male" Display “Female"


Java if/else Statement

20

String gender; : :if (gender.equals(“f”)) {

System.out.println(“Female”);}else{

System.out.println(“Male”);}

if(boolean expression) { statements to be executed if true } else { statements to be executed if false }


Nested IFs Having a decision structure inside a decision structure

Allows checking for multiple conditions

For example, insurance company assigns risk rating based on the type of car

21


Nested IFs

22

If (isCarType = "Sports") Then

If (isCarColor = "Red") Then

insType = "HighRisk"

Else

insType = "Normal"

End If

Else

insType = "Normal"

End If


Nested IFs

23

isCarType =

"Sports"

TrueFalse

isCarColor = "Red"

insType="HighRisk"

TrueinsType="Normal" False

insType="Normal"


Java Nested ifs

24

if (month == 1) { System.out.println(“Jan”);}

else {if (month == 2) { System.out.println(“Feb”);}

else { if (month == 3) { System.out.println(“Mar”);}

else { if (month == 4) {………

Nested if

Placing an if statement as one of the statements to be executed in an if/else clause


Case Structure

25

A large number of nested IFs can be difficult to understand/debug

The Case structure is an alternative

Use the keyword Select to identify the variable to be checked

Then the keyword Case followed by the value to check for


Case Structure

26

Select month

Case 1:

Display “Jan”

Case 2:

Display “Feb”

Case 3:

Display “Mar”

Etc. etc.

End Select


Case Structure

27

Can have a default case Identifies what to do if none of the checked values is true

Appears after all the Case statements

Select monthEtc. etc.Case 12:

Display “Dec”Default:

Display month, “ is not a valid value”End Select


Case Structure

28

lightColor

“Green”

Display “Stop”

Display “Maintain speed"

“Red”

Display “Punch it!"

“Yellow”


SFC Case Structure

29


SFC Case Structure

30

Click on circle to right of the Case symbol, then Edit, Insert

Specify the value to search for, then click OK


SFC Case Structure

31

Click on True circle and insert statements to perform if true


SFC Case Structure

32

Keep inserting cases until finished Of course, need to define lightColor and assign a value


SFC Case Structure

33


Raptor Case Structure

34

Doesn’t have one, must use nested IFs


Java Case Structure

35

Uses the keyword switch Very similar to the pseudo code in SFC

The value being checked is in parenthesis

Need break statements in each case because once the condition is true, all subsequent statements are executed

Copyright 2014 by Janson Industries36

Switch

switch (month) {

case 1: monthLabel.setText(“Jan”); break;

case 2: monthLabel.setText(“Feb”); break;

case 3: monthLabel.setText(“Mar”); break;

: : : : :

default: System.out.println(“Not a valid

month!”);

}

If there were no breaks: The label would be set to Dec The “Not a valid month” message would be displayed


Compound Condition Use AND or OR to connect many

conditions

Each AND & OR links two conditions

AND means both conditions must be true Replaces nested if

OR means either one or both conditions must be true Replaces multiple ifs

37


Compound Condition So instead of nested if:

38

If (isCarType == "Sports") Then If (isCarColor == "Red") Then insType == "HighRisk" Else insType == "Normal" EndifElse insType == "Normal"Endif

If (isCarType == "Sports" AND isCarColor == "Red") Then insType == "HighRisk"

Else insType == "Normal"

Endif


Compound Condition So instead of multiple ifs:

39

If (state == "WA") Then salesTaxRate = 0 EndifIf (state == "NJ") Then salesTaxRate = 0 Endif

If (state == "WA" OR state == "NJ") Then salesTaxRate = 0 Endif


Compound Condition If you specified the following

OR condition flavor == "vanilla" OR flavor ==

"chocolate"

And the ice cream man handed you a chocolate ice cream cone

Would the ice cream man have satisfied the condition?

40

YES


Compound Condition If you specified the following

AND condition flavor = ="vanilla" AND flavor ==

"chocolate"

And the ice cream man handed you a chocolate ice cream cone

Would the ice cream man have satisfied the condition?

41

NO


Truth Table Shows

2 conditions: x and y Every possible combination of T and F for x and y AND and OR compound condition Boolean value for each

combination

42

Cond x Cond y x AND y x OR y

True True True True

True False False True

False True False True

False False False False


Truth Table Two conditions:

Cond x: flavor == “Vanilla”

Cond y: coneType == “Sugar”

43

flavor coneType x AND y x OR y

Vanilla Sugar True True

Vanilla Waffle False True

Chocolate Sugar False True

Chocolate Waffle False False


Compound Condition Efficiency Conditions checked from left to

right

Short circuit evaluation stops checking in an AND as soon as a false condition is

found

OR as soon as a true condition is found

44


Compound Condition Efficiency If the programming language

supports short circuit evaluation

Specify the conditions so that the least amount of checks are performed

The fewer the checks, the faster the program will execute

45


OR Efficiency Put the condition that is most likely

to be true first in an OR condition

For instance, if 30% of sales come from NJ and only 5% from WA

Means that only 70% of the time is the 2nd condition checked Alternative would result in 2nd condition

being checked 95% of the time 46

If (state == "NJ" OR state == " WA") Then salesTaxRate = 0 Endif


AND Efficiency Put the condition that is most likely

to be false first in an AND condition

For instance, if 50% of customers are female and 90% are over 21

Means that only 50% of the time is the age checked Alternative would result in gender

being checked 90% of the time 47

If (gender == "F" AND age > 21) Then admissionType = "Free" Endif


Compound Condition Mistakes Most of the time specifying two

values for the same variable and connecting them with an AND carColor == "blue" AND carColor

== "red"

Means the condition can never be true How can the car color be both red

and blue?48


Compound Condition However using < or > and an

AND means you can search for ranges salary < 30000 AND salary >

20000

Means any salary from 20,001 to 29,999 would make the expression true

49


Compound Condition In SFC and Raptor use AND and

OR in the diamond shape

50


Here's the Java example of the compound AND condition

Java uses && for AND, || for OR (| is upper case \)

Prove by changing salary to 44000, compile, and run


Condition Mistakes Be careful with > and <

If we selected students for the dean's list with the following: gpa > 3.5

It would be incorrect because Students with gpa = 3.5 not selected

Selection should be gpa >= 3.5

52


Compound Condition Mistakes Also,

salary > 30000 AND salary < 20000 No salary value can make this true

salary < 30000 OR salary > 20000 Every salary value will make this true

Another mistake, not specifying a full condition

carColor = "blue" AND = "red" Need the variable carColor in the second

condition

53


Compound Condition Mistakes Unnecessary checks

No need to check if < 100000 a second time

54

If (salary >= 100000) Then

incomeTaxRate = .28

Else

If (salary < 100000 AND >= 60000) Then

incomeTaxRate = .25

End If

End If


Combining AND’s and OR’s The AND is evaluated first (from left to

right) then the OR

So if there were a car with the following characteristics color = "red", price = 16000, style = "sports"

And the condition was:

It would be evaluated as follows:

55

style = "sports" OR color = "red" AND price < 15000


Combining AND’s and OR’s

56

color = "red", price = 16000, style = "sports"

style = “sports” OR color = “red” AND price < 15000

style = “sports” OR True AND price < 15000

style = “sports” OR True AND False

style = “sports” OR False

True OR False

True


Combining AND’s and OR’s AND forms a strong bond between conditions

If there were a file full of cars and we printed only those cars that satisfied the condition:

57


Would we get a list of:

Sports cars and cheap red carsOr:

Cheap sports cars and cheap red cars


Combining AND’s and OR’s AND forms a strong bond between conditions

58


Means you will get a list of:

Sports cars and cheap red carsNot:

Cheap sports cars and cheap red cars

color = "red" AND price < 15000style = "sports" OR


To get a list of cheap sports cars and cheap red cars could specify:

Or (if parentheses are supported)

Combing AND’s and OR’s

59

style = "sports" AND price < 15000

color = "red" AND price < 15000

OR

(style = "sports" OR color = "red") AND price < 15000


Combining ANDs and ORs Three ice cream variables

flavor, container, topping

Person says give me Rocky Road AND Sugar Cone

OR Sprinkles OR Whip Cream

You hand over a Dish filled with Sprinkles

Did you satisfy the condition?60Yes


Combining ANDs and ORs Person says give me

Rocky Road AND Sugar Cone OR Sprinkles OR Whip Cream

You hand over a Rocky Road in a Dish

Did you satisfy the condition?

61

No


Combining ANDs and ORs Person says give me

Rocky Road AND Sugar Cone OR Sprinkles OR Whip Cream

You hand over a Rocky Road in a Dish with

Whip Cream

Did you satisfy the condition?

62

Yes


New Condition Check

63

Java example of the compound AND condition and inputting

data


Run twice and check both true and false legs


Conditions With many conditions, what to do

can get very complicated

Often flowchart or pseudocode hard to read

Alternative is a Decision table Shows conditions Every possible combination of

conditional values For each combination, what the

action(s) should be

65


Decision Table Example

66


Java example of the compound AND condition

and GUI

When run, dialog box pops up

Enter data, press OK

Problem: info read from dialog box is text. Have to convert to numeric with the parseInt function


Dialog box disappears and results shown in command prompt


Compound Conditions Design Ex Long distance charge basics:

Company charges 10 cents per minute for all calls outside the customer’s area code that last over 20 minutes

All other calls are 13 cents per minute

Want to create a program to calculate the cost of a phone call

69


Exercise Further info about program:

Accepts data about one phone call from user Customer area code (three chars) Customer phone number (eight chars) Called area code (three chars) Called number (eight chars) Call time in minutes (four digits)

Displays: All the inputted data Price for the call.

70


Compound Conditions Design Ex

What's the algorithm for this program?

71

Algorithm Answer


Compound Conditions Design Ex Long distance charge basics:

Company charges 10 cents per minute for all calls outside the customer’s area code that last over 20 minutes

All other calls are 13 cents per minute

What variables would a program need to handle this info? I.e. What are the important pieces of

information?

72Answer 2


Exercise

Create command prompt external design (XD) of this program

Answer 2.5

Create a GUI external design (XD) of this program

Answer 2.6

73


Exercise What is the pseudocode so far?

What is first command in pseudocode?

Where are variables defined?

How would you specify the variables?

74

Answer 3


SFC Exercise So in flow chart what is the first

symbol you enter?

Rectangle

What is text in rectangle?

75

Answer 4


Exercise After variables defined what's first

thing that has to happen (ignore the XD “formatting” for this example)

Read data in

What flow chart symbol?

76

Answer 5


Exercise Now what do we do?

Can we calculate price?

No have to figure type of call it is

What type of symbol is that?

77

Answer 6


Exercise

Now we can calculate price based on true or false


78

Answer 7


Exercise Now what?

Show the results


79

Answer 8


Exercise Pseudocode

80

Module mainDeclare String custAreaCode, custPhoneNum,

calledAreaCode, calledPhoneNumDeclare Integer minutesDeclare Real priceDeclare Real LOW_RATE = 0.10Declare Real HIGH_RATE = 0.13Declare Integer TIME_LIMIT = 20Input custAreaCode, custPhoneNum,

calledAreaCode, calledPhoneNum, minutesIf custAreaCode != calledAreaCode AND

minutes > TIME_LIMIT Thenprice = minutes * LOW_RATE

Elseprice = minutes * HIGH_RATE

End IfDisplay custAreaCode, custPhoneNum,

calledAreaCode, calledPhoneNum, priceEnd Module


Java Exercise

81

In java, always initialize variables

Strings to null String name = null;

Numbers to zero int price = 0;

To make a variable value fixed (unchangeable) define it as final

final double TAX_RATE = .065;


Java Exercise In java, must create a lot of stuff to read from command line

First, before the class header, you must import the following

import java.io.*;import java.util.Scanner;

public class ClassHeader {


Java Exercise Then in the main method, create the following variables and objects

Use the appropriate Scanner .next function Must assign read value to a variable

public static void main(String[] args) {Scanner keyboard = new Scanner(System.in);int numRead = 0;

numRead = keyboard.nextInt();


Java Exercise Reads (.next(), nextInt(), etc.) usually

paired with a prompt

: : : : : :System.out.println(“Please enter qty of purchase”);qty = keyboard.nextInt();System.out.println(“Please enter item price”);price = keyboard.nextDouble();total = price * qtySystem.out.println(“The transaction total is ” + total);

: : : : : :


Java Exercise

85

Write the java program to calculate the phone call cost and implement the command line XD

Answer 9


Java Exercise

86

Modularize the java program to calculate the phone call cost and implement the command line XD

Answer 10


Comparing Strings Some languages allow you to use

< and > to compare strings

Since all data stored as numbers (0’s and 1’s), some letters greater than others

A is less than B, B less than C, … Y is less than Z, Z is less than a, a is less than b, etc.

Java doesn’t allow <> with strings87


Boolean Variables Besides numeric and string

values there are Boolean values

Boolean values are true or false

There are also Boolean variables that can hold a Boolean value

Can use a Boolean variable in a condition instead of a Boolean expression

88


Boolean Variables

89

Module mainDeclare Integer hoursWorkedDeclare Real payRate, salaryDeclare Boolean isOvertimeDisplay “Enter number of hours worked ”Input hoursWorkedIf (hoursWorked > 40) Then

isOvertime = trueElse

isOvertime = falseEnd IfDisplay “Enter pay rate ”Input payRateIf (isOvertime) Then

salary = hoursWorked * (payRate * 1.5)

Elsesalary = hoursWorked * payRate

End IfDisplay “Salary is ”, salary

End Module


Points to Remember Decisions/selections require Boolean

expressions or variables

Boolean expressions result in a value of true or false

Use relational operator(s) to build Boolean expression

Can create compound conditions by combining Boolean expressions with AND and/or OR operators

90


Assignments Non-Graded

Chap 4 labs 3.1-3.4

Graded

Chap 4 lab 3.5

91

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