Object oriented programming slides for presentation

17/05/2025
Object Oriented Programming
W7 - L7

17/05/2025
Pointers
Overview:
Variable & MEMORY
 Computer memory is a collection of different memory locations.
 These memory locations are numbered sequentially.
 Each variable is created at a unique location in memory known as its address.
 A program may declare many variables.
 A variable declaration reserves specific amount of space in memory for a particular
variable.
 The variable name is used to refer to that memory location.
 It allows the users to access a value in the memory.
 The computer refers to the memory using address.

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 When we declare a variable three things are associated with that
variable
 Variable name
 Variable type
 Variable address

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Example:
Int main()
{
Int a;
Cout << “The address of a is: ” << &a;
Return 0;
}

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Can we store address of variable in
another variable?
Int main()
{
Int a;
Int b;
B = &a
Cout << “The address of a is: ” << &a;
Return 0;
}

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Pointer
 A pointer is a variable that is used to store a memory address.
 WHY we need Memory address when we can
use variable with their names?
 Pointers can access and manipulate data in
computer memory directly

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Advantages of Pointer:
 It can access the memory address directly.
 It can save memory
 It runs faster as it doesnot duplicate data.

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Example:
Int main()
{
Int n ;
Int *ptr ;
Cout << “enter an integer” ;
Cin >> n ;
Ptr = &n;
Cout << “the value of n is” << n ;
Cout << “the address of n” << ptr ;
Return 0;
}

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Void pointer(A void pointer is a pointer that has no associated data type with it. A void pointer
can hold address of any type and can be typecasted to any type)
// find output
Int main()
{
Int a = 10;
Float b = 10.5;
Char c = ‘a’ ;
Int *ptr;
Ptr = &a;
Cout << “address stored in pointer is : ” << ptr ;
}

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Find Error??
Int main()
{
Int a = 10;
Float b = 10.5;
Char c = ‘a’ ;
Int *ptr;
Ptr = &b;
}

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Void Pointer
Int main()
{
Int a = 10;
Float b = 10.5;
Char c = ‘a’ ;
void *ptr;
Ptr = &a;
Cout<<“value of a is:” << a;
Ptr = &b;
Cout<<“value of b is:” << b;
Ptr = &c;
Cout<<“value of c is:” << c;

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Dereference Operator: ( * )
In computer programming, a dereference
operator, also known as an indirection
operator, operates on a pointer variable. It returns
the location value, in memory pointed to by the
variable's value.

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Example:
Int main()
{
Int a = 20 ;
Int *ptr ;
Ptr = &a;
Cout << the value stored in pointer is: “ << *ptr ;
}

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Output :
 the value stored in pointer is: 20

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Data manipulation using Pointers
Int main ()
{
Int a , b , s , *p1, *p2 ;
P1 = &a ;
P2 = &b;
Cout << Enter an Integer : “ ;
Cin >> *p1;
Cout << Enter an Integer : “ ;
Cin >> *p2;
S = *p1 + *p2 ;
Cout << “sum is : ” << s;
}

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This pointer
 To know the address of current object , we use this pointer.
 Used to distinguished our data members and local variables when
both are declared with the same name.
 We identify the data member using this pointer

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Example:
Class person
{
Int age ;
String name ;
Person(int age , string name)
{
Age = age ; //compiler confusion
Name = name ;
}
Void printvalue()
{
Cout << “age” << age ;
Cout << “name” << name ;
}
};

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Int main ()
{
Person a(45 , “ABC”);
a.printvalue();
}

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Output:
 Garbage value

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Solution : this Pointer
Class person
{
Int age ;
String name ;
Person(int age , string name)
{
This ->Age = age ;
This ->Name = name ;
Void printvalue()
{
Cout << “age” << age ;
Cout << “name” << name ;
}
};

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Int main ()
{
Person a(35 , “abc”);
a.printvalue();
}

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Output :
 35
 abc

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Task:
 we have two data members num and ch.
 In member function setMyValues() we have two local variables having same name
as data members name.
 Create display function to show both values.
 In such case if you want to assign the local variable value to the data members
then you won’t be able to do until unless you use this pointer, because the compiler
won’t know that you are referring to object’s data members unless you use this
pointer.

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Solution:
#include <iostream>
using namespace std;
class Demo
{
private:
int num;
char ch;
public:
void setMyValues(int num, char ch)
{
this->num =num;
this->ch=ch;
}
void displayMyValues()
{
cout<<num<<endl; cout<<ch;
}
};
int main()
{
Demo obj;
obj.setMyValues(100, 'A');
obj.displayMyValues();
return 0;
}

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Polymorphism
 One name multiple forms
 Poly means many and morphism means forms
 The behaviour of the object can be implemented at rum time.
1. Compile time polymorphism
 Function overloading / method overloading / constructor overloading /
 operator overloading
2. Run time polymorphism
 virtual function
 Pointer to objects:
 pointer can also refer to an object of a class. The member of an object can
be accessed through pointers by using the symbol ->(member access
operator)
 Ptr->member

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Overview: // early binding compiler
already knows which function to call
Class A
{
Public: void show()
{
Cout<< “base class” ;
}
};
Derived Class
Class B: public A
{
Public: void show()
{
Cout<< “Derived
class” ;
}
};
Int main()
{
B obj;
Obj.show();
}
Output:

17/05/2025
Overview: // early binding
Class A
{
Public: void show()
{
}
};
Derived Class
Base class
Class B: public A
{
Public: void show()
{
Cout<< “Derived
class” ;
}
};
Int main()
{
B obj;
Obj.show();
Obj.A.show();
}
Output:

17/05/2025
Overview: // late Binding
Class A
{
Public: void show()
{
}
};
base class
Class B: public A
{
Public: void show()
{
Cout<< “Derived
class” ;
}
};
Int main()
{
A *ptr ;
A obj;
Ptr = &obj ;
Ptr - > show() ;
}
Output:

17/05/2025
Virtual Base class / Virtual Function :
 Key word virtual
 Virtual function is re defined in derived class.
 When a virtual function is defined in base class,
then the pointer to base class is created. Now
on the basis of type of object assigned the
respective class function is called.
 This is also called run time polymorphism.

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Virtual Function
 A virtual function (also known as virtual methods) is a member
function that is declared within a base class and is re-defined
(overridden) by a derived class.
 When you refer to a derived class object using a pointer or a
reference to the base class, you can call a virtual function for that
object and execute the derived class’s version of the method.

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Example: Class B : public A
{
Public:
Void show()
{
Cout << “Child Class B” ;
}
};
Class A
{
Public:
Void show()
{
Cout << “parent Class A” ;
}
};
Class C : public A
{
Public:
Void show()
{
Cout << “Child Class C” ;
}
};

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Int main ()
{
A obj1 ;
B obj2 ;
C obj3;
A *ptr;
Ptr = &obj1 ;
Ptr-> show() ;
Ptr = &obj2 ;
Ptr->show();
Ptr = &obj3;
Ptr->show();
}
Pointer can store address of child class , but
with the same pointer if we want to access
child class member that also exist in parent
class , this will always call member function of
parent class.

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Using virtual keyword:
One function is providing multiple functionalities depends on which
type of address , pointer is holding.

17/05/2025
Example: Class B : public A
{
Public:
Void show()
{
Cout << “Child Class B” ;
}
};
Class A
{
Public:
Virtual Void show()
{
}
};
Class C : public A
{
Public:
Void show()
{
Cout << “Child Class C” ;
}
};

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Int main ()
{
A obj1 ;
B obj2 ;
C obj3;
A *ptr;
Ptr = &obj1 ;
Ptr-> show() ;
Ptr = &obj2 ;
Ptr->show();
Ptr = &obj3;
Ptr->show();
}

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Working:
 When a member function is declared as a virtual in parent class and is
called with pointer , the compiler checks the type of object referred by
the pointer. It executes the member function according to the type of
object not by type of pointer.
 The type of pointer in each call is different so the compiler executes
different function each time.

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Binding:
 Binding refers to the process of converting identifiers (such as variable and
performance names into addresses.)
 Binding is done for each variable and functions.
 For functions, it means that matching the call with the right function
definition call by the compiler.
 Binding can be performed in two ways:
 Early binding/compile time binding/ static binding(As the name indicates
compiler directly associate an address to the function call. In early binding,
compiler knows at the time of compilation which block of code is to be
executed upon a function call.)
 Late binding/ Dynamic binding(in late binding, compiler does not know at
the time of compilation that which block of code is to be executed upon a
function call. Late binding is attained by using virtual functions.)

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Early Binding
 Is also called compile time binding or static binding
 As the name indicates, compiler directly associate an address to
the function call.
 In early binding , compiler knows at the time of compilation which
block of code is to be executed upon a function call.

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Example: Early Binding
Class A
{
Public:
Void show()
{
}
};
Class B : Class A
{
Public:
Void show()
{
Cout << “Derived Class B” ;
}
};
Int main()
{
B obj ;
Obj.show();
Obj.A.show();
}

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Late Binding
 In late binding compiler doesn’t know at the time of compilation that
which block of code is to be executed upon a function call.
 Late binding is attained using virtual function .

17/05/2025
Example :
Class parent
{
Public:
Virtual void show()
{
Cout<< “parent
class” ;
}
};
Class child1: public parent
{
Public:
void show()
{
Cout<< “child1 class” ;
}
};

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Class child2: public parent
{
Public:
void show()
{
Cout<< “child2 class” ;
}
};

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Int main()
{
Parent *ptr[5] ; // array of pointers
//This pointer can store address of child class address .
Int op , i ;
// for object creation
Cout << “Enter 1 for parent , 2 for child1 & 3 for
child2” ;

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For (I = 0 ; I < 5 ; i++)
{
Cout << “which object to create ?” ;
Cin >> op ;
If (op == 1)
Ptr[i] = new parent ; // create new object of parent
Else if (op ==2)
Ptr[i] == new child1;
Else (op ==3)
Ptr[i] == new child2;
}

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For (I = o ; I <5 ; i++)
{
Ptr[i] -> show();
It will call that function whose class object address is stored in pointer
array.
}

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 What if we remove virtual keyword?
 What will be the output ??

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Abstract class(Model class) and
pure Virtual function
 No definition of virtual function assigned with zero.
 We can’t create the object of parent class having pure virtual
function
 If we don’t override the function in child class that was present in
abstract class then the child class will also become abstract class.

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Pure virtual function

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Output:
Child1 class…
Child2 class…

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