Week 03 b

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Week 03 - b

• Control Structures
• Decisions

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Sample Programs Referenced(code located in
course folder)

• PigLatin
• ComputeTax
• RollTheDice

• MissingBreak
• Simple Calculator
• GUI Calculator
• DaysInMonth
• OrdinalSuffix

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Hint on ReadingGrade Counts for HW 3

• import javax.swing.
• public class GradeBreakdown extends Applet
• private int numA, numB, numC, numD, numF
• public void init()
• numA Integer.parseInt(
• JOptionPane.showInputDialog(
• "Number of A's?"))
• numB Integer.parseInt(
• JOptionPane.showInputDialog(
• "Number of B's?"))
• . . .
• // end of init method
• . . .
• // end of GradeBreakdown applet

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Control Structures

• Regulate flow of execution in a program or method
• Individual instructions combined into a single
  logical unit with
• One entry point
• One exit point
• 3 Types of Control Structures
• Sequence
• Selection
• Repetition (later)

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Sequence

• A compound statement group of statements
  bracketed with curly braces
• statement1
• statement2
• statementn
• Statements executed sequentially
• That's what we've been doing

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Selection

• A selection is made
• whether to execute a statement, or
• which of some alternative statements will be
  executed
• Makes possible program design in which some
  statements may be skipped, and other statements
  executed
• Selection is based on some logical criteria
• if (bankBal lt 0)
• System.out.println( Deposit some money! )
• else
• System.out.println( Balance is bankBal )

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Flowcharts
balance lt 0
yes
no
display deposit
display balance
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if Statement

• Ensures that a statement is executed only when a
  condition is true
• Conditions typically involve comparison of
  variables or quantities for equality or
  inequality
• Syntax
• if ( condition )
• statement
• Example
• if (age gt 18)
• out.println(Eligible to vote.)

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if Statement with Optional else

• An if statement may have an optional else clause
  that will only be executed when the condition is
  false
• Syntax
• if ( condition )
• statement
• else
• statement
• Example
• if (wages lt FICA_LIMIT)
• tax FICA_TAX_RATE wages
• else
• tax FICA_TAX_RATE FICA_LIMIT

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PigLatin "unionway ollegecay"BlueJ

• public class PigLatin // modified from
  Koffman Wolz page 206
• private String word
• public PigLatin(String word)
• this.word word
• // end of PigLatin constructor
• private boolean firstLetterVowel()
• final String VOWELS "aeiouyAEIOUY"
• char first word.charAt(0)
• return (VOWELS.indexOf(first) gt -1)
• // end of firstLetterVowel method
• public String translateWord()
• if (firstLetterVowel()) return word "way"
• else return word.substring(1)
  word.charAt(0) "ay"
• // end of translateWord method
• public String toString()
• return word
• // end of toString method
• // end of PigLatin class

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Compound Alternatives

• To execute more than one statement conditionally,
  you may use to define a compound statement
  for either (or both) conditional alternatives
• Example
• given two numbers, divide the larger by the
  smaller
• compute both quotient and remainder

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Compound Alternatives

• if (firstNumber lt secondNumber)
• quotient secondNumber / firstNumber
• remainder secondNumber firstNumber
• // end of ltfirst number is smallergt
• else
• quotient firstNumber / secondNumber
• remainder firstNumber secondNumber
• // end of ltsecond number is smallergt

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Danger Semicolon Ahead

• What would happen in the following code?
• if (p gt q)
• out.println("p gt q")
• How about
• if (x 5)
• out.println("x equals 5")
• else
• out.println("x not equal to 5")

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"Dangling" else Problem

• Code written
• if (condition-1)
• if (condition-2)
• statement-1
• else
• statement-2

• Interpreted as
• if (condition-1)
• if (condition-2)
• statement-1
• else
• statement-2

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Use to solve Dangling else

• if (condition-1)
• if (condition-2)
• statement-1
• else
• statement-2

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Representing Complex Logic
pseudocode

• enter PIN
• if PIN correct
• enter amount
• if balance gt amount
• dispense
• else
• refuse request
• else
• shred card!

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Nesting if-else Statements

• Example
• if (condition-1)
• statement-1
• else
• if (condition-2)
• statement-2
• else
• statement-3

• Another format
• if (condition-1)
• statement-1
• else if (condition-2)
• statement-2
• else
• statement-3

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Multi-alternative Decisions

• Assign a letter grade for a course according to
  the table ?
• 5 alternatives
• How do we structure the logic?
• 5 separate decisions?
• A set of cascading decisions?
• How do we implement the logic in Java?

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Compare Java Code

• if (numGrade gt 90)
• letterGrade A
• if (numGrade gt 80 numGrade lt 90)
• letterGrade B
• if (numGrade gt 70 numGrade lt 80)
• letterGrade C
• if (numGrade gt 60 numGrade lt 70)
• letterGrade D
• if (numGrade lt 60)
• letterGrade F

• if (numGrade gt 90)
• letterGrade A
• else if (numGrade gt 80)
• letterGrade B
• else if (numGrade gt 70)
• letterGrade C
• else if (numGrade gt 60)
• letterGrade D
• else
• letterGrade F

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Java Code

• boolean exam_improved (ex1 lt ex2)
  (ex2 lt ex3)
• boolean hwk_improved (hw1 lt hw2)
  (hw2 lt hw3)
• if (exam_improved)
• if (hwk_improved)
• out.println(Great overall improvement!)
• else
• out.println(Great exam improvement!)
• else if (hwk_improved)
• out.println(Great homework improvement!)

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calcTaxBlueJ

• public class Payroll
• private double weeklyPay
• public Payroll(double newPay)
• weeklyPay newPay
• // end of GREATLY SIMPLIFIED Payroll
  constructor
• public double calcTax()
• double taxAmount
• if (weeklyPay gt 2000.00)
• taxAmount 0.35 weeklyPay
• else if (weeklyPay gt 1000.00)
• taxAmount 0.28 weeklyPay
• else if (weeklyPay gt 500.00)
• taxAmount 0.20 weeklyPay
• else if (weeklyPay gt 100.00)
• taxAmount 0.15 weeklyPay
• else
• taxAmount 0.00
• return taxAmount

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Tracing if/else with BlueJ

• Run the Payroll program
• View the Debugger
• Set a breakpoint at the start of the if
  structure, and step through the code

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RollTheDiceBlueJ

• public class RollTheDiceApp
• public static String checkDice()
• int die1, die2, dice
• die1 (int)(6Math.random() 1)
• die2 (int)(6Math.random() 1)
• dice die1 die2
• System.out.println("Dice roll " dice)
• if (dice 7 dice 11)
• return "You Win!"
• else if (dice 2)
• return "Snake Eyes!"
• else
• return "Try Again."
• // end of checkDice
• public static void main(String args)
• System.out.println(" " checkDice())
• System.out.println(" " checkDice())
• System.out.println(" " checkDice())

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HW 3 Hint 2

• Create a generic drawBar method which you call 5
  times (once for each letter grade)
• num on next slide would refer to argument to
  method
• Send it the vertical bar position for the
  particular letter
• drawBar(A, numA, 200, g)
• drawBar(B, numB, 250, g)
• drawBar(C, numC, 300, g)
• drawBar(D, numD, 350, g)
• drawBar(F, numF, 400, g)

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HW 3 Hint 3

• private void drawBar(String ltr, int num,
  int vertical, Graphics g)
• if (num max5(numA,numB,numC,numD,numF))
• g.setColor(Color.GREEN)
• else if (num min5(numA,numB,numC,numD,numF))
• g.setColor(Color.RED)
• else
• g.setColor(Color.BLACK)
• g.drawString(ltr, 20, vertical15)
• g.fillRect(40, vertical, 5num, 25)
• // end of drawBar method
• NOTE You would also need to write methods max5
  and min5 with 5 int arguments.
• Within your max5 you could use nested calls to
  Math.max(int,int)
• Math.max(a,Math.max(b,Math.max(c,Math.max(d,f))))

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To the Computers...

• Help on HW 3 if you need it

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Java BREAK
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More Multi-Way Decisions

• Menu problems
• User presented with a list of choices
• User asked to enter a letter or number to
  represent that choice
• The program executes code depending on choice
• Example
• Ask the user for two real numbers and a choice of
  whether to add, subtract, multiply, divide the
  numbers
• Produce the result of the chosen operation

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Algorithm

• get the two numbers
• display a menu of operations
• get the operation
• if the operation is
• compute the result first number second number
• else if the operation is
• compute the result first number - second number
• else if the operation is
• compute the result first number second number
• else if the operation is /
• compute the result first number / second number
• display the result

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Coding Questions

• How should we represent the operation?
• English word?
• Character?
• Integer?
• How should we implement the decision structure?
• Set of one-way ifs
• Cascading (nested) ifs
• Is there another way?

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The Old-Fashioned TV switch
Streamlined Multiway Decisions
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The switch Statement

• Used to accomplish multi-way branching based on
  the value of an integer selector variable
• Recall that char type is interpreted as integer
• Syntax
• switch ( expression )
• case value1 statements
• case value2 statements
• case valuen statements
• default statements
• // end of switch

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Switch Warning

• Java switch statements exhibit drop-through
  behavior.
• 1. Expression is evaluated.
• 2. If Expression ConstantValuei Control jumps
  to the Statement after ConstantValuei.
• 3. Control continues within the switch statement
  until
• a. The end of the switch is reached (i.e. )
• b. A break is executed, terminating the switch
• c. A return is executed, terminating the
  function or
• d. An exit(0) is executed, terminating the
  program.

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Why is break used in switch statements?(MissingBr
eak in BlueJ)

• Consider the code fragment below
• int i 1
• switch (i)
• case 0 System.out.print("zero")
• case 1 System.out.print("one")
• case 2 System.out.print("two")
• case 3 System.out.print("three")
• // end of switch(i)
• System.out.println( )
• Without breaks the output is ???

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Pick the Appropriate Vehicle

• switch (numOfPassengers)
• case 0 ...println(The Harley)
• break
• case 1 ...println(The Dune Buggy)
• break
• default ...println(The Humvee)
• // end of switch(numOfPassengers)

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Comparing switch and if statements

• if equivalent
• switchValue expression
• if (switchValue value1)
• statement1
• else if (switchValue value2)
• statement2
• else if (switchValue valuei)
• statementi
• else
• statement(i1)

• switch statement
• switch (expression)
• case value1 statement1 break
• case value2 statement2 break
• case valuei statementi break
• default statement(i1)

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Calculator ProgramBlueJ

• Replace
• cascading
• if statements
• with a switch
• See SimpleCalculator program

• validOp true
• if (op '')
• result firstNum secondNum
• else if (op '-')
• result firstNum - secondNum
• else if (op '')
• result firstNum secondNum
• else if (op '/')
• result firstNum / secondNum
• else
• validOp false

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GUI CalculatorBlueJ

• private String doCalculation()
• try
• int a Integer.parseInt(registerA)
• int b Integer.parseInt(registerB)
• int result 0
• switch (operator)
• case '' result a b break
• case '-' result a - b break
• case '' result a b break
• case '/' result a / b break
• default return " E R R O R"
• // end of switch
• return ("" result)
• // end of try
• catch (Exception e)
• System.out.print('\u0007') // beep
• return " E R R O R"
• // end of catch
• // end of doCalculation method

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Symbolic Constants in switch Statements

• final int
• SUNDAY 1, MONDAY 2, TUESDAY 3,
• WEDNESDAY 4, THURSDAY 5, FRIDAY 6,
• SATURDAY 7
• int day String strDay
• ...
• switch (day)
• case SUNDAY strDay Sunday break
• case MONDAY strDay Monday break
• case TUESDAY strDay Tuesday break
• case WEDNESDAY strDay Wednesday break
• case THURSDAY strDay Thursday break
• case FRIDAY strDay Friday break
• case SATURDAY strDay Saturday break
• System.out.println(strDay)

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Multiple case Labels in switch Statements

• switch (day)
• case MONDAY
• case WEDNESDAY
• case FRIDAY
• Ssytem.out.println(Math meets at 900
  today)
• System.out.println(History meets at 1000
  today)
• break
• case TUESDAY
• case THURSDAY
• System.out.println(CS meets at 915 today)
• System.out.println(Chemistry meets at 200
  today)
• break
• default
• System.out.println(Enjoy the weekend!)
• // end of switch(day)

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Calculate Days in a Month

• Input month and 4-digit year
• "30 days hath September" and all that
• Need to worry about Leap Years for February
• Years that are evenly divisible by 400, or are
  evenly divisible by 4 and not by 100

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Is it a Leap Year?

• if ((year 400 0)
• ((year 4 0) (year 100 ! 0)))
• then it is a leap year
• else
• it is not a leap year

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Days In Month?BlueJ

• import javax.swing.
• public class DaysInMonthApp
• public static void main(String args)
• int month Integer.parseInt(JOptionPane.showI
  nputDialog("Month?"))
• int year Integer.parseInt(JOptionPane.showIn
  putDialog("Year?"))
• System.out.println("Days in Month "
  daysInMonth(month,year))
• // end of main method
• private static boolean leapYear(int year)
• return (year400 0) (year4 0
  year100 ! 0)
• // end of leapYear method
• private static int daysInMonth(int mon, int yr)
  
• switch (mon)
• case 9 case 4 case 6 case 11
• return 30 // note no break needed
• case 2
• if (leapYear(yr))
• return 29
• else
• return 28

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Letter Grade to Grade Points

• double gradePoints(char grade, char plusMinus)
• double gp
• switch (grade)
• case 'A' gp 4.0 break
• case 'B' gp 3.0 break
• case 'C' gp 2.0 break
• case 'D' gp 1.0 break
• case 'F' gp 0.0 break
• default gp -1.0
• // end of "grade" switch
• switch (plusMinus)
• case '' gp 0.3 break
• case '-' gp - 0.3 break
• // end of "plusMinus" switch
• return gp
• // end of gradePoints method

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Ordinal SuffixBlueJ

• Write an application to read an integer n between
  0 and 100, and write n followed by the
  appropriate ordinal suffix
• (20th, 21st, 23rd, or 22nd).
• How do we start? What are the rules?
• Implementation nested if? switch?
• See OrdinalSuffix

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To the Computers...

• Try GUI "Calculator"
• Some features have not been covered as yet
• button clicking events, etc.
• Drag from course folder to My Documents

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Java BREAK