2. oop with c++ get 410 day 2

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2Object Oriented Programming

04/11/23


Making a member variable “static”

For a static Member variable, individual copies of each member

are not made for each object.

No matter, how many objects of class are instantiated, only one

copy of static data member exists

All objects of that class will share same variable.

When we declare a static data member within a class, we are not

defining it. i.e. not allocating any storage for it.

Ideally, We need to provide a global definition outside the class. This

is done by re-declaring static variable using ::

Static Members of a Class

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Static member is initialized to zero when first object is created.

Static members are typically created to maintain values common to

entire class.

Like – to maintain a counter that counts the occurences of all the

objects.

Just like a static member, we can also have static member function

Which can have access to only other static members.

Which is invoked by using class name rather than object


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class item{ static int count; int price;

public :

item() { price=100;

}


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void incr() { price++; count++; } void show() { cout<<" \nPrice "<<price; cout<<" \nCount = "<<count; } };int item :: count ;


void main(){ clrscr(); item a,b,c; cout<<" \n\n A's Show"; a.show(); cout<<" \n\n B's Show"; b.show(); cout<<" \n\n C's Show"; c.show();


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a.incr(); b.incr(); c.incr(); cout<<" \n\n A's Show after INCR";a.show();cout<<" \n\n B's Show after INCR";b.show();cout<<" \n\n C's Show after INCR";c.show();getch(); }

price 100

a

price 100

b

price

c

100

0

Count

101101 101

123

void incr()

{

price++;

count++;

}


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Basic approach to accomplish Code Reuse here is

Do not recreate the existing class from a scratch

Use or Extend existing class which is proven

You simply create objects of your existing class inside new class

New class is composed of objects of existing class.

COMPOSITION

You create a new class as a type of existing class.

Take the basic form of existing class and simply add new code to it and

that too, without modifying existing class.

INHERITANCE

Influential Reuse Mechanisms in C++

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Actually we have already been composing the classes

Primarily with Built-In Types.

It turns out to be almost as easy to use composition

With user defined types, typically with classes.

Composition

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class date {

};

class person { char name[20];

};

int dd, mm, yy ; date DOB


The syntax of Composition was quite obvious.

Now --------- A new approach to perform Inheritance

Just say ------ “ This New Class is like that Old Class “

New Class : Existing Class

New Class is said to be derived from Existing Class .

Where as Existing Class works as Base Class for New Class.

When we explore like this ----------------- we involuntarily make

specific part of base class accessible to derived class.

Of course ---------- without impacting the protection mechanism of

encapsulation.

Inheritance

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Inheritance

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class person { char name[20];

};

date DOB

class analyst : public emp {

float incentives;

};

class date {

};

int dd, mm, yy ;

class emp : public person {

int Empid;

};


Class Hierarchy and Relationships

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Person DateHas - a

Employee

Is - a

Analyst

Is - a


Obviously, we should not construct a derived class without calling the

base class constructor.

It either happens implicitly, if it is a Non – Argument Constructor

Mechanism.

The Base Class Constructors are called implicitly in the opening stage of

Derived Class Constructor.

Virtually, the first line of derived class constructor would be the call to the

Base Class Constructor.

For the Parameterized Constructor, it’s other way round. We need to

follow separate mechanism known as “Constructor Chaining”. Here

we specify Constructor’s Initialization List.

Constructors & Parameter List in Inheritance

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Base Class Access Specifier Gimmicks

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Private Members of Base Class

• Can not be inherited• Not accessible for derived class directly• Not accessible for outside environment

Public Members of Base Class

• Directly available for derived class• Accessible for outside environment also.

Protected Members of Base Class

• Directly available for derived class• Not Accessible for outside environment.


Visibility Mode – Specifies how the features of the base class are

derived.

Private Derivation - class emp : private person

When a Base Class is privately inherited by derived class, ‘Public Members ‘

of Base Class become ‘Private Members’ of Derived Class.

So Public Members of Base Class can only be accessed by member functions

of derived class. They are inaccessible to the objects of derived class

Public Derivation - class emp : public person

When a Base Class is publicly inherited by derived class, ‘Public Members ‘

of Base Class become ‘Public Members’ of Derived Class also.

They are accessible to objects of derived class.

Derivation Variants - Visibility Mode

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Protected Derivation - ?????

Derivation Variants - Visibility Mode

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Inheritance Variants

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Class A

Class B

Simple Inheritance

Class B Class C

Class A

Class DClass C

Multilevel Inheritance

Multiple Inheritance

Hybrid Inheritance

Multipath Inheritance


Here 3 variants of Inheritance are involved - Simple / Multiple / Multilevel Derived Class D has 2 direct base classes ‘Class B’ & ‘Class C’Which themselves have a common base class ‘Class A’ --- Indirect Base ClassClass D inherits the traits of Indirect Base Class via two separate paths.All Public & Protected Members of Class A are inherited into Class D twice.Class D would have duplicate sets of inherited members from Class A causing ambiguity.This can be avoided by making the common base class as Virtual Base Class

Consequence of Multipath Inheritance

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Class B Class C

Class A

Class D

Multipath Inheritance


When a class is made a Virtual Base Class, Compiler takes necessary care to see that only one copy of that class is inherited, regardless of how many inheritance paths exist

Virtual Base Class

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Class A { …..; };

Class B1 : virtual public A { …..; };

Class B2 : public virtual A { …..; };

Class C : public B1, public B2 { …..; };


Class Hierarchy and Relationships

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Person Date

Employee

SM Programmer Admin

Empid, Basic

AllowanceProject name, Passport Details, Km, CPK

Target, Commission Passport Details, Km, CPK


SM S1 ("Sachin", 4, 6, 1968, 2001, 10000, 120000, 0.05, "S121314", 100,200);

Admin A1 ("Abhay", 12, 12, 1990, 3001, 5000, 5000);

Prog P1("Prasad", 10, 10, 1985, 4001, 25000, ”Railway Reservation System", "P212223", 100,200);

Emp arr[3]

arr[0] = s1; arr[1] = A1; arr[2] = P1

Create methods to show all employee details, to get total travelling expenses and to get total salary.

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Bank maintains 2 kinds of Accounts --- Savings & CurrentSaving Acct provides 4% Interest But no Cheque BookCurrent Acct provides Cheque Book But no interest. Also insist for Minimum Balance of Rs 5000. Penalty of Rs 500 can be imposed for Non-maintenance of Minimum BalanceCreate a class Account which stores Name, Acct No & Acct Type. Further derive Curr_Acct & Sav_Acct to make them more specific to requirement.Include Necessary Member Functions To Perform Menu Driven Activity as Follows

1. Accept deposi and Update Balance2. Display Customer Info with Balance 3. Compute & deposit the interest4. Permit withdrawal and Update Balance5. Check Minimum Balance & impose the penalty to update balance

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Derived(formal parameter list, parameter to base class constr.) : Base(Its Parameter) { Activity in Derived class Constructor }

In the Hierarchy of Date ------- Person --------- Emp

emp e1(2001, 25000, “Sachin”) – This is Object Creation

emp(int emp1, float emp2, char *person1) : person(person1) { } - This is Derived Class Constructor

person(char *person1) { } - This is Base Class Constructor

Constructors & Parameter List in Inheritance

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