SELECTION II

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SELECTION II

• CSC 171 FALL 2004
• LECTURE 9

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Sequential statements
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Block
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Simple Branching
If (test) A
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test
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Branching
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If (test) A else B
test
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Structured Programming

• Using structures as building blocks

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• if (maritalStatus single)
• if (income lt 21450.0)
• taxRate .15
• else
• taxRate .27
• else
• if (income lt 86500.0)
• taxRate .28
• else
• taxRate .31

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• if ((maritalStatus single)
• (income lt 21450.0)) taxRate .15
• if ((maritalStatus single)
• (income gt 21450.0)) taxRate .27
• if ((maritalStatus ! single)
• (income lt 86500.0)) taxRate .28
• if ((maritalStatus ! single)
• (income gt 86500.0)) taxRate .31

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• double rich String effct
• if (richt gt 8.0)
• effct most structures fall
• else if (richt gt 7.0)
• effct many buildings destroyed
• else if (richt gt 6.0)
• effct some buildings damaged
• else if (richt gt 4.5)
• effct some damage to poor construction
• else if (richt gt 3.5) effct no damage
• else if (richt gt 0) effct not felt much

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• int gNum String gName
• if (gNum 1) gName freshman
• if (gNum 2) gName sophomore
• if (gNum 3) gName junior
• if (gNum 4) gName senior
• else gName unmatriculated

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• int gNum String gName
• if (gNum 1) gName freshman
• if (gNum 2) gName sophomore
• if (gNum 3) gName junior
• if (gNum 4) gName senior
• else gName unmatriculated

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Switch Statement

• Test cases must be constant
• Test cases must be integers
• Test is

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T
break
F
T
break
F
default
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• int gNum String gName
• switch(gNum)
• case 1 gName freshman break
• case 2 gName sophomore break
• case 3 gName junior break
• case 4 gName senior break
• default gName unmatriculated break

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• int gNum String gName
• if (gNum 1) gName freshman
• if (gNum 2) gName sophomore
• if (gNum 3) gName junior
• if (gNum 4) gName senior
• else gName unmatriculated

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• int gNum String gName
• switch(gNum)
• case 1 gName freshman
• case 2 gName sophomore
• case 3 gName junior
• case 4 gName senior
• default gName unmatriculated
• // everyone is unmatriculated

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The Selection operator

• Semantics (3 operands)
• lttestgt ? ltvalue1gt ltvalue2gt
• Usually, Shorthand for
• if (lttestgt) x y else x z
• Which can be written as
• x lttestgt ? y z

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Absolute Value of x

• int x, absoluteX
• x myGetInt()// some user input
• absoluteX (x gt 0) ? x -x
• Instead of
• if (x gt0) absoluteX x
• else absoluteX -x

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SimpleTaxes

• double income, taxRate
• income myGetd()// user input
• taxRate (income gt 120000.0)
• ? 0.31 0.40
• Instead of
• if (income gt 120000.0)
• taxRate .31 else taxRate .41

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Sample Problem Democracy

• We expect record voter turnout, this election
• In order to make things run smoothly
• Democrats vote on Wednesday
• Everyone else votes on Tuesday
• We have been asked to write a program to help get
  these instructions out

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Just for fun

• Write an implicit if operator that sets a
• String called votingInstruction to
• Vote on Wednesday if the string called
  registration is set to Democrat, otherwise
  set votingInstruction to Vote on Tuesday

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Helping Democracy

• System.out.println(What party are you?)
• String registration console.readline()
• String votingInstruction
• ((registration.equals(Democrat) ?
• Wednesday Tuesday)
• System.out.println(You should vote on
• votingInstruction)