C.S.U.B. Computer Science
Michael Sarr

CMPS 2020

Reading

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private versus public versus protected
File: private_protected_private_members.h 

class A
{
public:
    int x;

protected:
    int y;

private:
    int z;

public:
void SetX(int in){x = in;}// any class function can access public members
void SetY(int in){y = in;}// any class function can access protected members
void SetZ(int in){z = in;}// any class function can access private members


};


 
class B : public A
{
// x is public
// y is protected
// z is not accessable at all even by member functions

// SetX, SetY and SetZ are sill accessable 


};



int main()
{


A one;

one.x =55;  // valid, its public
one.y =200; // not valid, protected members are not accessable outside the class;
one.z =300; // not valid, protected members are not accessable outside the class;


one.SetX(1);// valid, the function is public 
one.SetY(2);// valid, the function is public 
one.SetZ(3);// valid, the function is public 




B two;

two.x = 5; // valid
two.y = 10; // not valid, protected members are not accessable outide the class
two.z = 15; // not valid we can even access z directory from functions of the class

two.SetX(5);// valid
two.SetY(10);// valid 
two.SetZ(15);// valid









} 





ONLY public data members and public functions can be called or accessed from outside the class ( in our main.cpp )

member functions have full access to all public , private and protected data members




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Inheritance 

when you define a class in c++ you can inherit from it and create similar classes 
this is usefull to create something similar to a class you have already but add some more data members or change the behavior slightly

for example 
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File: Automobile.h 

#ifndef AUTOMOBILE_H
#define AUTOMOBILE_H
#include <string>
using namespace std;

// The Automobile class holds general data
// about an automobile in inventory.
class Automobile
{
protected:
   string make;   // The auto's make
   int model;     // The auto's year model
   int mileage;   // The auto's mileage
   double price;  // The auto's price

public:
   // Default constructor
   Automobile()
   {  make = "";
      model = 0;
      mileage = 0;
      price = 0.0; }
               
   // Constructor
   Automobile(string autoMake, int autoModel,
              int autoMileage, double autoPrice)
   {  make = autoMake;
      model = autoModel;
      mileage = autoMileage;
      price = autoPrice; }
   
   // Accessors
   string getMake() const
   { return make; }
   
   int getModel() const
   { return model; }
   
   int getMileage() const
   { return mileage; }
   
   double getPrice() const
   { return price; }
};
#endif





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now we can create the car class and use Automobile as its parrent class
the car will "inherit" from its parent 
it will have all the data members and functions as an Automobile but we will add in 
int doors as well as an accessor function and an additional constructor

File: Car.h 

#ifndef CAR_H
#define CAR_H
#include "Automobile.h"
#include <string>
using namespace std;

// The Car class represents a car.
class Car : public Automobile
{
private:
   int doors;
   
public:
   // Default constructor
   Car() : Automobile()
   { doors = 0; }
   
   // Constructor #2
   Car(string carMake, int carModel, int carMileage,
       double carPrice, int carDoors) :
       Automobile(carMake, carModel, carMileage, carPrice)
   { doors = carDoors; }
   
   // Accessor for doors attribute
   int getDoors()
   { return doors; }
};
#endif




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now we can create the SUV class and use Automobile as its parrent class
the car will "inherit" from its parent 
it will have all the data members and functions as an Automobile but we will add in 
int passengers as well as an accessor function and an additional constructor

File: SUV.h 

#ifndef SUV_H
#define SUV_H
#include "Automobile.h"
#include <string>
using namespace std;

// The SUV class represents a SUV.
class SUV : public Automobile
{
private:
   int passengers; 
   
public:
   // Default constructor
   SUV() : Automobile()
   { passengers = 0; }
   
   // Constructor #2
   SUV(string SUVMake, int SUVModel, int SUVMileage,
       double SUVPrice, int SUVpassengers) :
       Automobile(SUVMake, SUVModel, SUVMileage, SUVPrice)
   { passengers = SUVpassengers; }
   
   // Accessor for passengers attribute
   int getPassengers()
   { return passengers; }
};
#endif






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data members can be public, protected or private

and a class has inheritance levels of
public, protected and private as well 
File: private_protected_private_inheritance.h 







you can think of the inheritance level in terms of escalation

if  you use public inheritance 
public and protected data members and functions will stay as they are 

if you use protected inheritance... any inherited members or functions will be escalated to at least protected


if you use private inheritance... any inherited members or functions will be escalated to at least private



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