Difference between revisions of "Advanced-C++/C2/Abstract-Class/English"

• Abstract Classes
• Pure virtual function
• We will do this through an example.

• Ubuntu OS version 11.10
• g++ compiler v. 4.6.1

Abstract class is used as a base class.

It contains at least one pure virtual function.

We cannot create an instance of abstract class.

A pure virtual function is a function with no body.

It is not defined in the base class.

It is declared as follows:

virtual void virtualfunname()=0;

A derived class must override the function.

Otherwise the compiler will give an error.

It is upto a derived class to implement the function.

I have already typed the code on the editor.

Note that our filename is abstract.cpp

This example involves addition and subtraction of two numbers.

abstract.cpp

#include<iostream>

using namespace std;

class abstractinterface

public:

virtual void numbers()=0;

It is initialized to 0.

void input();

int a, b;

And two integer variables as a and b.

void abstractinterface::input()

{

cout<< "Enter the numbers\n";

cin>>a>>b;

}

In this we accept the numbers a and b.

class add : public abstractinterface

It inherits the properties of the base class "abstractinterface".

public:

void numbers()

{

int sum;

sum=a+b;

cout<<"sum is "<<sum<<"\n";

}

In this we perform addition of two numbers a and b.

And store the result in integer variable "sum".

Then we print the result.

class sub : public abstractinterface

{

public:

This also inherits the base class "abstractinterface".

void numbers()

{

int diff;

diff=a-b;

cout<<"diff is "<<diff<<"\n";

}

And here we calculate the difference of two numbers a and b.

Then we print the difference.

int main()

add obj1;

obj1.input();

obj1.numbers();

Then we call both the functions "input" and "numbers" using the object obj1.

sub obj2;

obj2.input();

obj2.numbers();

Again, we call the two "functions using the object obj2.

return 0;

Ctrl, Alt and Tkeys simultaneously

g++ abstract.cpp -o abs

To execute

Type

./abs

g++ abstract.cpp -o abs

Press Enter

Type:

./abs

Press Enter

Output

Enter the numbers

I will enter as 9 and 4.

The output is displayed as Sum is 13

Again we see Enter the numbers.

I will enter as 8 and 3.

The output is displayed as Diff is 5

Come back to our slides.

Summary

In this tutorial we learnt,

Abstract class

eg. class abstractinterface

Pure virtual function

eg. virtual void numbers()=0;

Assignment

• Create an abstract class student.

• Create a pure virtual function as Info

• Accept the name and roll no of the student in the function.

• Create two derived class marks and sports.

• In marks, accept marks of three subjects.

• In sports, enter marks scored in sports.

• Calculate the total marks.

• Then create another derived class result.

I*n this, display the name, roll-no, total marks of the student.

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