Default Construtor

[Himanshu Chawla]

Ques : Define the class Book with all the basic attributes such as title, author, publisher, price etc. Define the default constructor, member functions display_data() for displaying the Book details. Use appropriate access control specifiers in this program

I have done some part

#include<iostream.h>
#inlude<conio.h>
using namespace std;
class book
{
char author, publisher, price ,ibn;

of the program .. but i am not getting the concept of Default contructor .. Please help me in understanding it by giving an example .. it to complicated as i have readd on stackoverflow.com , on ibm website and other websites also .. but i am getting confused and confused. Please Help me ..?? and please help in solving the rest part of my program ..??

[phorce]

Your default constructor is the definition in which you will initialise your objects from. (in main usually)

Your default constructor looks like the following:

P.S. It is also worth noting that the class name should always be capitialised as this is a good coding practise, so, Book instead of book with that being said, your class should look like the following:

class Book {

    public:
        Book(); // Default constructor 

    private:

        char author, publisher, price ,ibn;
};

You should also make the access specifiers clear, i.e. public, private, protected

Hope this helps.

[rubberman]

Also, specifying each element as a char means they only can have one character! I suspect that you don't want to do that... :-)

Use this (or something similar):

class Book {
    private:
        std::string author, publisher, ibn;
        double price;
    public:
        Book(); // Default constructor 
};

[kal_crazy]

What goes into a default constructor? Is it an empty function? Or can we set private members with a value?
For eg.

Book(){

author = "Some Name";
}

[phorce]

Yes you can do the following. But, your default constructor should be left. Then, you can use method overriding to pass values through.

[kal_crazy]

But, your default constructor should be left.

Should be left? Empty?

[mark5rockzz_1]

Default constructor will only exist if you do not provide your own manually hence the compiler will make a constructor for you (that's why it's called DEFAULT constructor)because in OOP manner, you cannot instantiate a new object without providing any constructor of that class.
Suppose you make an instance of class Rectangle
code:

class Rectangle
{
private:
    int width;
    int height;
public:
    Rectangle() : width(0), height(0) //initializer list
    {
    //both `width` and `height` will have an initial value of 0
    }
};

Rectangle rect; //you have just call `Rectangle()!`
//now rect.width == 0 && rect.height == 0!


hope this helps

[kal_crazy]

That helped :)

[Himanshu Chawla]

First of all ... Thanxs to everyone for supporting me and giving me asnwers ..
by the answer of mark5rockzz_1 i have completly understand the question and phorce's answer has also helped me a lot.... thank u very much...!!!!

[Himanshu Chawla]

Sorry i forgot to thank rubberman... its was a good answer and i understand it..!!