Karels Sensory Equipment

1
Karels Sensory Equipment

• This PPT originated with Dr. Roland Untch
• Modifications have been made by Dr. Cripps

2
Karels Sensory Equipment

• Karel has three video cameras, a microphone, a
  compass, and tactile sensors to help him stay out
  of trouble. He can request information from his
  sensory equipment
• frontIsClear, frontIsBlocked, nextToABeeper, etc.
• Each request will result in a true or false
  answer. Questions that can be answered as either
  true or false are called predicates.

3
Decision statements

• Karel can check predicates, i.e., you can ask
  Karel a question, by using what is called an IF
  construct. These constructs can be used wherever
  instructions are used in a program. In the C/C
  language, there are two variations of the IF
  statement
• The simple IF
• The compound IF-THEN-ELSE

4
The Simple If

• if (predicate)
• ltthen-clause statement(s)gt

• If the predicate is true the statements in the
  then clause are executed followed by the
  instructions immediately after the then clause,
  i.e, after the
• If the predicate is false, then the statements in
  the then clause are not executed and we jump to
  the instruction immediately following the then
  clause, i.e, after the

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Karels Predicates

• frontIsClear
• leftIsClear
• rightIsClear
• facingNorth
• facingSouth
• facingEast
• facingWest
• nextToABeeper
• noBeepersInBeeperBag

• frontIsBlocked
• leftIsBlocked
• rightIsBlocked
• notFacingNorth
• notFacingSouth
• notFacingEast
• notFacingWest
• notNextToABeeper
• anyBeepersInBeeperBag

6
Examples the Simple IF

• if (nextToABeeper)
• PickBeeper()
• if (frontIsClear)
• Move()
• TurnLeft()

• if ( frontIsClear )
• Move()
• TurnLeft()
• if (nextToABeeper()
• PickBeeper()
• void FaceNorthIfFacingSouth()
• if (facingSouth)
• TurnLeft()
• TurnLeft()

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Compound If

• if(predicate)
• ltthen-clause statement(s)gt
• else
• ltelse-clause statement(s)gt

• If the predicate is true, the instructions in the
  then clause are executed then the instruction
  immediately after the then clause
• If the predicate is false, the instructions in
  the else clause are executed then the instruction
  immediately after the then clause

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Examples of Compound IF

• void FaceNorthIfFacingSouthOrEast()
• if (facingSouth)
• TurnLeft()
• TurnLeft()
• else
• if ( facingEast )
• TurnLeft()

• if (frontIsClear)
• Move()
• else
• TurnLeft()

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• void Escape()
• if (frontIsClear)
• Move()
• TurnLeft()
• else
• TurnLeft()
• Move()

• void GiveOrTake()
• if (nextToABeeper)
• if (anyBeepersInBeeperBag)
• PutBeeper()
• else
• PickBeeper()

10
Braces can be omitted when the then or else
clause contains only one statement

• Original code
• if (nextToABeeper)
• PickBeeper()
• Move()

• with braces omitted
• if (nextToABeeper)
• PickBeeper()
• Move()

11
Examples the Simple IF Revised

• if (nextToABeeper)
• PickBeeper()
• if (frontIsClear)
• Move()
• TurnLeft()

• if ( frontIsClear )
• Move()
• TurnLeft()
• if (nextToABeeper()
• PickBeeper()
• void FaceNorthIfFacingSouth()
• if (facingSouth)
• TurnLeft()
• TurnLeft()

12
Examples of Compound IF revised

• void FaceNorthIfFacingSouthOrEast()
• if (facingSouth)
• TurnLeft()
• TurnLeft()
• else if ( facingEast )
• TurnLeft()

• if (frontIsClear)
• Move()
• else
• TurnLeft()

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• void Escape()
• if (frontIsClear)
• Move()
• TurnLeft()
• else
• TurnLeft()
• Move()

• void GiveOrTake()
• if (nextToABeeper)
• if (anyBeepersInBeeperBag)
• PutBeeper()
• else
• PickBeeper()