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 atleast 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 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

Simultaneously on your keyboard.

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.

In this display the name, roll-no, total marks of the student.

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