OOPs

Inheritance in C++

link

The capability of a class to derive properties and characteristics from another class is called Inheritance

Sub Class/Derived Class: The class that inherits properties from another class is called Sub class or Derived Class. Super Class/Base Class:The class whose properties are inherited by sub class is called Base Class or Super class.

Syntax:

class class_name: access_specifier base_class_name {
    //body
};

Modes of Inheritance

Example

class base 
{
	public:
		int x;
	protected:
		int y;
	private:
		int z;
};

class publicDerived: public base
{
	// x is public
	// y is protected
	// z is not accessible from publicDerived
};

class protectedDerived: protected base
{
	// x is protected
	// y is protected
	// z is not accessible from protectedDerived
};

class privateDerived: private base
{
	// x is private
	// y is private
	// z is not accessible from privateDerived
}

In the above example, we observe the following things:

• base has three member variables: x, y and z which are public, protected and private member respectively.
• publicDerived inherits variables x and y as public and protected. z is not inherited as it is a private member variable of base.
• protectedDerived inherits variables x and y. Both variables become protected. z is not inherited If we derive a class derivedFromProtectedDerived from protectedDerived, variables x and y are also inherited to the derived class.
• privateDerived inherits variables x and y. Both variables become private. z is not inherited If we derive a class derivedFromPrivateDerived from privateDerived, variables x and y are not inherited because they are private variables of privateDerived.

Types of Inheritance

• Single: Normal waali, gfg
• Multiple: link
  • Class inherits from multiple classes
  • Constructors are called in same order, in which they are inherited, exampul in link
  • The destructors are called in reverse order of constructors.
  • Diamond Problem: Occurs when two base class of class have a common base class, check link
    • Constructor and destructor called two times
    • Solution is virtual class
• Multilevel: gfg
  • Derived class is created from derived class, A->B->C
• Hierarchical : gfg
  • More than one derived class from base class, ek baap ke ek se zyada bacche.
• Hybrid: gfg
  • Combining more than one inheritance, eg: Combining Hierarchical and multiple inheritance.

Questions from notes or search by yourself

Virtual base class

Link

As seen in multiple inheritance

Suppose you have two derived classes B and C that have a common base class A, and you also have another class D that inherits from B and C. You can declare the base class A as virtual to ensure that B and C share the same subobject of A. A virtual base class ensures that only one copy of that class is inherited.

Polymorphism in C++

• Having many forms, concept of Object Oriented Programming.
• Example, Real life example of polymorphism, a person at a same time can have different characteristic. Like a man at a same time is a father, a husband, a employee. So a same person posses have different behavior in different situations. This is called polymorphism.

Two types:

1. Compile Time polymorphism
   • Achieved by function overloading or operator overloading.
     • Function Overloading:
       • Multiple functions with same name but different parameters. Funtions can be overloaded by change in number of arguments or type in arguments.
       • Link
       • Rules of Function Overloading
     • Operator Overloading
       • Overloading operators, like +, -, (), etc.
       • Link
       • Syntax: return_type operator + ()
2. Runtime Polymorphism
   • Function Overriding