How to sort objects using friend function in C++?

A Beginner's Guide to Creating a Virtual Function in C++

A Beginner's Guide to Creating a Virtual Function in C++

Virtual Function: A virtual function is a member function that is declared within base class and is re-defined by derived class. Virtual functions ensure that the correct function is called for an object, regardless of the type of reference (or pointer) used for function call. Functions are declared with a virtual keyword in base class. They are mainly used to achieve Runtime polymorphism. The resolving of function call is done at Run-time. It is used to tell the compiler to perform dynamic linkage or late binding on the function.

Rules for Virtual Function

1.Virtual functions must be members of some class.
2.Virtual functions cannot be static members.
3.They are accessed through object pointers.
4.They can be a friend of another class.
5.A virtual function must be defined in the base class, even though it is not used.
6.The prototype of virtual functions should be same in base as well as derived class.

How To Use without Virtual Keyword in C++?.

#include<iostream> using namespace std; class A { public: void area() { int h=20; int w=30; int a=h*w; cout << "A class Area:"<<a; } }; class B: public A { public: void area() { int h=20; int w=30; int a=h*w; cout << "B class Area:"<<a; } }; int main() { A* a; B b; a = &b; a->area(); } *****OUTPUT***** A class Area:600

How To Use with Virtual Keyword in C++?

#include<iostream> using namespace std; class A { public: virtual void area() { int h=20; int w=30; int a=h*w; cout << "A class Area:"<<a; } }; class B: public A { public: void area() { int h=20; int w=30; int a=h*w; cout << "B class Area:"<<a; } }; int main() { A* a; B b; a = &b; a->area(); } *****OUTPUT***** B class Area:600

Pure Virtual Function: A virtual function is not used for performing any task. It only serves as a placeholder. When the function has no definition, such function is known as the "do-nothing" function. The "do-nothing" function is known as a pure virtual function. 

A pure virtual function is a function declared in the base class that has no definition relative to the base class. A class containing the pure virtual function cannot be used to declare the objects of its own, such classes are known as abstract base classes. 

The main objective of the base class is to provide the traits to the derived classes and to create the base pointer used for achieving the runtime polymorphism.

Pure Virtual Function can be declared in C++?

#include<iostream> using namespace std; class A { public: virtual void area()=0; { int h=20; int w=30; int a=h*w; cout << "A class Area:"<<a; } }; class B: public A { public: void area() { int h=20; int w=30; int a=h*w; cout << "B class Area:"<<a; } }; int main() { A* a; B b; a = &b; a->area(); } *****OUTPUT***** B class Area:600

Friend Function: A Friend function is defined as a friend function then, the private and protected data of a class can be accessed using the function. The complier knows a given function is a friend function by the use of the keyword friend. 

For accessing the data, the declaration of a friend function should be made inside the body of the class (can be anywhere inside class either in private or public section) starting with keyword friend.

Syntax of friend function

class className { friend return_type functionName(argument); } return_type functionName(argument) {  // Private and protected data of className can be accessed from // this function because it is a friend function of className. }

How To Use friend function in C++?

#include<iostream> using namespace std; class Box { public: int h; int w; int area; Box() { h=10; w=10; } friend void area(Box); }; void area(Box f) {  f.area=f.h*f.w; cout<<"Area of Box:"<<f.area; }  int main() { Box b; area(b); } *****OUTPUT***** Area of Box:100

Friend Class: A friend class is a class that can access the private and protected members of a class in which it is declared as friend. This is needed when we want to allow a particular class to access the private and protected members of a class.

How To Use Friend Class in C++?

#include <iostream> using namespace std; class A { int x=100; friend class B; }; class B { public: void display(A &a) {  cout<<"Value of x is : "<<a.x; }   };  int main() { A a; B b; b.display(a); return 0; } *****OUTPUT***** Value of x is :100

Static Variable: When a variable is declared with static keyword ,it is called static variable. When a variable is declared as static, space for it gets allocated for the lifetime of the program. 

Even if the function is called multiple times, space for The static variable is allocated only once and the value of variable in the previous call gets carried through the next function call.
For better understanding see the example below

How To Use without static keyword in C++?

#include <iostream> using namespace std; void A() {  int i = 0;   cout << i << " "; i++; } int main() { A();   A();    A();   A();   } *****OUTPUT***** 0 0 0 0

How To Use with static keyword in C++?

#include <iostream> using namespace std; void A() { static int i = 0;   cout << i << " "; i++; } int main() { A();   A();    A();   A();   } *****OUTPUT***** 0 1 2 3

Static Function: When a function is declared with static keyword is called static function. It can be called by class name directly using scope resolution(::). There is no need of object to call a static function.

How To Use Static Function in C++?

#include <iostream> using namespace std; class A { public: static void B() { cout<<"I am inside static function"; } }; int main() { A::B(); } *****OUTPUT***** I am inside static function

Exception: To understand the exception firstly we should know about the error in prgram.Errors in program can be categorized into two types.

1.Compile Time Errors

2.Run Time Errors

Compile Time Errors: Errors caught during compiled time is called Compile time errors. Compile time errors include library reference, syntax error or incorrect class import.

Run Time Errors: The error that occours during the run time of program is called run time error.
They are also known as exceptions. Hence we can say that exception is a runtime error that occours because of user's mistake.

Reasons of Exception: Mismatched Input: Suppose that we are entering our name in place of age, causing exception because age is of data type int and name will be string.

File does not exist : Suppose that we are reading a text file easy.txt and that file does not exist in the system, causing exception.

Exception related to array : Suppose that the array size is 5 and we are inserting more than 5 elements, causing exception.

Divide by zero exception : When a number is divided by zero then the output will be undefined(infinity).

Exception Handling: The process of handling the exception is called exception handling. There are three main keyword are used to solve the problem of exception.

try block : It is the place where actual code is written and exception occours. when the code will lead to any error, that error/exception will get caught inside the catch block.

catch block : catch block is intended to catch the error and handle the exception condition. We can have multiple catch blocks to handle different types of exception and perform different actions when the exceptions occur.
throw statement : It is used to show the user defined message about the exception.

Syntax of try-catch

Try { // protected code } catch( ExceptionName e1 ) {  // catch block } catch( ExceptionName e2 ) { // catch block }  catch( ExceptionName en ) { // catch block }

How To Use Exception Handling in C++?

#include<iostream> using namespace std; void Exception(int x,int y) { try { if(y!=0) { int z=x/y; cout<<"Division Value:"<<z; } else throw "Don't put zero in denominator"; } catch(const char *s) { cout<<s; } } int main() {  int a,b; cout<<"Enter a value:"; cin>>a; cout<<"Enter b value:"; cin>>b; Exception(a,b); } *****OUTPUT***** Enter a value:10 Enter b value:2 Division Value:5 Second Run Program Enter a value:10 Enter b value:0 Don't put zero in denominator