The document discusses abstract classes and polymorphism in C++. It provides examples of: 1. Defining an abstract base class Linear Data Structure (LDS) with pure virtual functions like push() and having derived classes Stack and Queue implement these functions. 2. Using polymorphism through pointers and references to the base class to call push() on either Stack or Queue objects. 3. A similar example with an abstract base class Shape and derived classes Rectangle and Circle implementing the area() function polymorphically.

1. Mohammed Sikander
Team Lead
CranesVarsity
Mohammed.sikander@cranessoftware.com

2. STACK
 void push(int )
 void pop( )
 bool empty( )
 int & top( )
QUEUE
 void push(int)
 void pop( )
 bool empty( )
 int &front( )
Sikander 2

3. STACK
 Push: Increment top Index and
add the element at top
 Pop : Delete the element at top
and decrement top Index
 Empty: If top Index is -1; Stack is
empty
 int & top( )
QUEUE
 Push: Increment rear Index and
add the element at rear
 Pop : Delete the element at front
and increment front Index
 Empty : If front Index is greater
than rear Index; Queue is empty
 int &front( )
Sikander 3

4. int main( )
{
int dschoice ,ch , ele;
cout << "1. Stack 2. Queue n";
cin >> dschoice ;
if(dschoice == 1)
{
Stack s1;
for( ; ; ) {
cout <<"StackOperations n";
cout <<"1. Push n 2. Pop 3. Display n";
cin >> ch;
switch(ch) {
case 1 : cout <<"Enter the element to push : ";
cin >> ele;
s1.push(ele);
break;
case 2 : if(s1.empty() == true)
cout <<"Stack is empty n";
else
s1.pop( );
break;
case 3 : s1.display( );
}
}
}
Sikander 4
else
{
Queue q1;
for( ; ; )
{
cout <<"QueueOperations n";
cout <<"1. Push n 2. Pop 3. Display n";
cin >> ch;
switch(ch)
{
case 1 : cout <<"Enter the element to push : ";
cin >> ele;
q1.push(ele);
break;
case 2 : if(q1.empty() == true)
cout <<"Queue is empty n";
else
q1.pop( );
break;
case 3 : q1.display( );
} //End of Switch
} //End of For
} //End of else
} //End of Main

5. Sikander 5
LDS
Stack Queue
• Stack is a Linear Data Structure
•Queue is a Linear Data Strucuture

6. class LDS
{
};
Sikander 6
class Stack : public LDS
{
public : void push(int ele);
};
classQueue : public LDS
{
public : void push(int ele);
};
int main( )
{
LDS *ptr = new Stack; //Valid
ptr->push( 5 ); // Invalid; as we don’t have push in LDS
}

7. class LDS
{
public : virtual void push(int ele);
};
Sikander 7
class Stack : public LDS
{
public : void push(int ele);
};
classQueue : public LDS
{
public : void push(int ele);
};
int main( )
{
LDS *ptr = new Stack; //Valid
ptr->push( 5 ); // No Compilation Error
// Linker Error
}

8. class LDS
{
public : virtual void push(int ele) = 0;
};
Sikander 8
class Stack : public LDS
{
public : void push(int ele);
};
classQueue : public LDS
{
public : void push(int ele);
};
int main( )
{
LDS *ptr = new Stack; //Valid
ptr->push( 5 ); // No Compilation Error, No Linker Error
//Invokes push of Stack.
ptr = new Queue;
ptr->push(6); //Invokes push of Queue
}

9. class LDS
{
public: virtual void push(int ) = 0;
virtual void pop( ) = 0;
virtual void display( ) = 0;
virtual bool empty( ) = 0;
};
class Stack : publicLDS
{
public: void push(int ) { cout << “Stack Push n”;}
void pop( ) ;
void display( ) ;
bool empty( ) ;
};
classQueue : public LDS
{
public: void push(int ) { cout << “Queue Push n”;}
void pop( ) ;
void display( ) ;
bool empty( ) ;
};
Sikander 9
int main( )
{
int dschoice ,ch , ele;
LDS *ptr;
cout << "1. Stack 2. Queue n";
cin >> dschoice ;
if(dschoice == 1)
ptr = new Stack;
else
ptr = new Queue;
for( ; ; ) {
cout <<"1. Push n 2. Pop 3. Display n";
cin >> ch;
switch(ch) {
case 1 : cout <<"Enter the element to push : ";
cin >> ele;
ptr->push(ele);
break;
case 2 : if(ptr->empty() == true)
cout <<“Empty n";
else
ptr->pop( );
break;
case 3 : ptr->display( );
}
}
}

10. void dsoperations(LDS &ref);
int main( )
{
int dschoice ,ch , ele;
LDS *ptr;
Stack s1;
Queue q1;
cout << "1. Stack 2.Queue n";
cin >> dschoice ;
if(dschoice == 1)
dsoperations(s1);
else
dsoperations(q1);
}
Sikander 10
void dsoperations(LDS &ref)
{
for( ; ; ) {
cout <<"1. Push n 2. Pop 3. Display n";
cin >> ch;
switch(ch) {
case 1 : cout <<"Enter the element to push : ";
cin >> ele;
ref.push(ele);
break;
case 2 : if(ref.empty() == true)
cout <<“Empty n";
else
ref.pop( );
break;
case 3 : ref.display( );
}
}
}

11. class Shape
{ public : virtual int area( ) = 0;
};
class Rectangle : public Shape
{ int m_l , m_b;
public :
Rectangle(int l , int b ) : m_l(l) , m_b(b)
{ }
int area( ){
return m_l * m_b;
}
};
class Circle : public Shape
{ int m_radius;
Public : Circle(int r) : m_radius( r )
{}
int area( )
{
return 3.14 * m_radius * m_radius;
}
}
Sikander 11
int main( )
{
Shape *ps = new Rectangle(4 , 5);
cout << ps->area( );
ps = new Circle(6);
cout << ps->area( );
}

12. class Shape
{
public : virtual int area( ) = 0;
};
class Rectangle : public Shape
{
int m_l , m_b;
public : Rectangle(int l , int b )
{
m_l = l , m_b = b;
}
int area( ){
return m_l * m_b;
}
};
Sikander 12
int main( )
{
Rectangle r(4 , 5);
Shape &s = r;
s.area( );
}

13. classA
{
public : virtual void display( ) = 0;
};
voidA::display( )
{
cout <<“A display n”;
}
int main( )
{
}
Sikander 13