CH5 Conditional Statements

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CH5 Conditional Statements

• Flavor 1
• if ( ltsome boolean expressiongt )
• ltsome instruction listgt

For now these are method invokations (see next
slide)
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IF
predicates either Tor F
frontIsClear() nextToABeeper() nextToARobot() f
acingNorth() facingSouth() facingEast() facingW
est() anyBeepersInBeeperBag()

• if ( )

Robot
Lets check the API to see our options
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Robot Class

• public class Robot extends UrRobot
• public boolean frontIsClear()
• public boolean nextToABeeper()
• public boolean nextToARobot()
• etc

Now I have a brain!
again, you dont write this class
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Examples

• if ( karel.frontIsClear() )
• karel.move() // no danger of hitting wall

if ( karel.anyBeepersInBeeperBag()
) karel.putBeeper() // no danger of error
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Extending Robot

• public class SmartBot extends Robot
• public boolean beeperIsToLeft()
• public boolean twoBeepersOnCornerOrMore()
• public void faceEast()

Draw the Inheritance Hierarchy
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• public boolean beeperIsToLeft()
• turnLeft()
• move()
• if ( nextToABeeper() )
• turnLeft() turnLeft() move()
  turnLeft() return true
• turnLeft() turnLeft() move() turnLeft()
• return false

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you write twoBeepersOnCornerOrMore()it belongs
to the SmartBot classnote you may have to nest
if statements
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you write faceEast()it belongs to the SmartBot
class
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Paying Attention?

• For the last several slides, Ive lead you
  somewhat astray. By now (Im hoping) someone has
  pointed out that our Inheritance Structure looks
  likes this

What annoying thing (should have) happened to you
while coding the last few examples?
Yep, you wrote (or wanted to) turnRight() and
maybe even turnAround() AGAIN! ANNOYING!
Solution(s)?
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Boolean Operators

• Same as C (, , !)
• Karel (Java) Robot (, , !)
• if (! frontIsClear())
• turnLeft()
• move()

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and (no, I didnt stutter)

• Write this method
• /
• _at_returns true if there is at least
• one beeper on both sides of bot,
• false otherwise
• /
• public boolean isBeepOnLeft_And_BeepOnRight()
• Assume that the class youre writing this for has
  SmartBot as its superclass (the one we just
  suggested). It may help to look at the
  inheritance tree again.

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IF - ELSE

• Flavor 2
• if ( ltboolean expressiongt )
• ltstatementsgt
• else
• ltstatements somewhat differentgt

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IF ELSE Simplifications

• simplify
• if ( frontIsClear() )
• return true
• else
• return false

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Simplify

• if ( ! leftIsBlocked() )
• return true
• else
• return false

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Simplify

• if ( leftIsBlocked() )
• return false
• else
• return true

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Simplify bottom factoring
move()
move()

• if ( facingSouth() )
• turnLeft()
• move()
• else
• turnRight()
• move()

if ( facingSouth() ) turnLeft() else turn
Right()
move()
move()
move()
move()
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Simplify top factoring

• if ( beeperOnLeft() )
• move()
• turnLeft()
• else
• move()
• turnRight()

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being redundant again and again and againha ha

• if ( facingNorth() )
• move()
• pickTwoBeepers()
• if (facingNorth())
• turnLeft()