CIS05 Comparative Languages Objects as function parameters

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CIS05 Comparative LanguagesObjects as function
parameters

• Marc Conrad
• D104a (Park Square Building)
• Marc.Conrad_at_luton.ac.uk
• These slides
• Three ways to pass a parameter in C.

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Example The Athlete class.

• include ltiostreamgt
• class Athlete
• private
• char lastName20
• int fitness
• public
• Athlete(char theName)
• sprintf(lastName, theName)
• fitness 0
• void jump()
• fitness fitness 1
• stdcout ltlt lastName ltlt
• " jumps" ltlt stdendl
• void displayFitness()
• stdcout ltlt "Fitness of " ltlt lastName
• ltlt " is " ltlt fitness ltlt
  stdendl

• The state of the athlete is defined by
• name
• fitness
• Behaviour
• jump
• display fitness.
• The athlete becomes fitter when he jumps.

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Call by Value Copying

• include "Athlete.h"
•  
• void doExercise(Athlete who, int howMuch)
• for( int i 0 i lt howMuch i )
• who.jump()
•  
• int main()
• Athlete fabian("Fabian")
• doExercise(fabian, 5)
• fabian.displayFitness()
• return 0

• The object fabian is copied.
• Not fabian jumps but a copy of fabian.

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Call by Value but Pointer!

• include "Athlete.h"
•  
• void doExercise(Athlete who, int howMuch)
• for( int i 0 i lt howMuch i )
• who-gtjump()
•  
• int main()
• Athlete fabian("Fabian")
• doExercise(fabian, 5)
• fabian.displayFitness()
• return 0

fabian

• A pointer to the object fabian is copied.
• Via the pointer we can access the fabian object
  and make it jump.

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Call by Reference
Output

• include "Athlete.h"
•  
• void doExercise(Athlete who, int howMuch)
• for( int i 0 i lt howMuch i )
• who.jump()
•  
• int main()
• Athlete fabian("Fabian")
• doExercise(fabian, 5)
• fabian.displayFitness()
• return 0

O.k
who

• The fabian object is passed by reference.
• The object is not copied and can be accessed
  without using pointers.

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Passing ParametersSummary

• Basically C has three ways to pass objects as
  function parameters
• Pass by value The object is copied.
• Pass a pointer A pointer to the object is
  copied.
• Pass by reference A reference to the object
  allows to access the object directly.
• Question How does it compare to C and Java?