CSCI 1302

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CSCI 1302

• Object-Oriented Programming
• Intermediate C

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Agenda

• Parameter passing (ref, out, value)
• Static
• Const
• Overloading
• Inheritance

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Parameter Passing

• By default, parameters are passed by value
• A copy of the value is passed
• The original is not modifiable
• Use ref to create by-reference parameter
  passing
• A reference to the value is passed (akin to a
  pointer)
• The original (actual) parameter is modifiable
• Use out when data is strictly coming out of
  (and being created in) the function
• The original has no value
• A new value will be placed into the parameter by
  the function

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By Value Parameter Example

• float CalculateCost (float unit_cost, int
  how_many)
• return unit_cost how_many
• static void Main()
• ...
• line_cost CalculateCost(uc, hm)
• ...

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By Value Parameter Example

• float CalculateCost (float unit_cost, int
  how_many)
• return unit_cost how_many
• static void Main()
• ...
• line_cost CalculateCost(uc, hm)
• ...

Even if you changethese locally, they
wontchange in Main.
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By Reference Parameter Example

• void UpdateGrade (ref float grade, float factor)
• grade factor
• static void Main()
• ...
• for(i0 i lt grades.Count() i)
• UpdateGrade(gradesi, 0.05)
• ...

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By Reference Parameter Example

• void UpdateGrade (ref float grade, float factor)
• grade factor
• static void Main()
• ...
• for(i0 i lt grades.Count() i)
• UpdateGrade(gradesi, 0.05)
• ...

Grade will be updatedinformation is taken
inand modifies the original
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Out Parameter Example

• void ReadChoice (out int choice)
• do
• Console.WriteLine("Please enter a choice 1-4
  ")
• choice Int32.Parse(Console.ReadLine())
• while ((choice lt 1) (choice gt 4))
• static void Main()
• ...
• ReadChoice(c)
• ...

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Out Parameter Example

• void ReadChoice (out int choice)
• do
• Console.WriteLine("Please enter a choice 1-4
  ")
• choice Int32.Parse(Console.ReadLine())
• while ((choice lt 1) (choice gt 4))
• static void Main()
• ...
• ReadChoice(c)
• ...

Choice is generated inthe module and
thenreturned to Main
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Static

• Each instance of a class (called an object) has a
  copy of the attributes
• Changing an attribute in one object doesnt
  affect the attribute of another object
• But what if we want persistence (shared) among
  all instances?

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Static Variables

• void PrintNumbers ()
• static int count 0
• Console.WriteLine(count)
• count
• static void Main()
• ...
• for(i0 i lt 50 i)
• PrintNumbers()
• ...

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Static Attributes

• class BMW_Z4
• public static int VehicleId 0
• ...
• static void Main()
• ...
• BMW_Z4 my_z4 new BMW_Z4() // has VehicleId
  of 0
• BMW_Z4 your_z4 new BMW_Z4() // has VehicleId
  of 1
• ...

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Const

• Variables are just that variable
• They can be changed programmatically via the
  assignment operator ()
• But there are times when some values should be
  immutable
• Preface the declaration with const
• Cannot be changed EVER!

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Const Example

• class BMW_Z4
• public const int MaxSpeed 185
• private int currentSpeed
• public void Accelerate
• currentSpeed 5
• if (currentSpeed gt MaxSpeed)
• currentSpeed MaxSpeed
• ...

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Overloading

• Overloading involves using the same
  method/function name
• Vary the number of parameters
• Vary the type of parameters
• Cannot just change return type (ambiguity in
  invocation)
• Useful to keep things simple
• Squaring a number

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Overloading Example

• int Square (int i)
• return i i
• float Square (float i)
• return i i
• static void Main()
• ...
• float x Square(5.3)
• int y Square(9)
• ...

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OperatorOverloading

• class BMW_Z4
• ...
• public BMW_Z4 ()
• Initialize(0, 2004, false)
• public BMW_Z4 (int my)
• Initialize(0, my, false)
• private Initialize(int cs, int my, bool tu)
• currentSpeed cs
• ModelYear my
• TopUp tu

Notice same methodname, differentparameters
Place commoninitialization in aseparate function
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Inheritance

• Inheritance allows one class to take on the
  properties of another
• Superclass-subclass relationship
• Sometimes called parent-child relationship
• Use the keyword extends to express this
  relationship
• Subclass will inherit certain attributes and
  methods
• Benefit good design, reuse of code

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Class Hierarchy
Mammal
int weight
giveBirth( )
Land-Mammal
int numLegs
Question how many attributes does Dog have?
Dog
boolean rabid
Chihuahua
SheepDog
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Things to Note

• Land-Mammal is a superclass to Dog, but a
  subclass to Mammal
• Dog has three attributes
• weight, numLegs and rabid
• Two from inheritance, one it declared itself

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Visibility and Inheritance

• Public allows all to see
• Private allows only class in which defined to
  see
• Protected allows class and all subclasses that
  inherit to see
• Consequently, well now use protected instead of
  private by default (common)

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C Syntax

• class Person
• ...
• class Student Person
• ...
• class Professor Person
• ...

Notice the use of
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The Base Class Object

• All classes in C inherit (sometimes implicitly)
  from Object
• Includes common set
• ToString()
• GetType()
• Equals()
• Often useful to override (implement) these
  virtual functions
• public override string ToString()

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FIN