Finally.

I finally learned Classes.

Since i finished being comfortable with them today , i decided to make a little application.

Here it is.

main.cpp

Code:

#include "Library.h"

using namespace std;



int main()
{

	Dog dog;

	string enterdogname;
	string enterdogcolor;
	int enterdogweight;


	cout <<"Hello, What's your dog name? "<<endl;
	cout <<">>";
	cin >> enterdogname;
	cout <<"\n\n";
 
	dog.setName(enterdogname);
	system("cls");

	cout <<"What color is your dog?"<<endl;
	cout <<">>";
	cin >> enterdogcolor;
    cout <<"\n\n";

	dog.setColor(enterdogcolor);
	system("cls");

	cout <<"What's is the weight of your dog?"<<endl;
	cout <<">>";
	cin >> enterdogweight;
	cout <<"\n\n";

	dog.setWeight(enterdogweight);
	system("cls");

	cout <<"Dog name: "<<dog.getName()<<endl;
	cout <<"Dog color: "<<dog.getColor()<<endl;
	cout <<"Dog weight: "<<dog.getWeight()<<endl;
	cout <<"Press enter to reset your dog informations";
	cin.get();
	cin.get();
    
	dog.reset();
	system("cls");

	cout <<"Let's check if your dog informations has been reset.Press enter again."<<endl;
	cin.get();

	cout <<"Dog name: "<<dog.getName()<<endl;
	cout <<"Dog color: "<<dog.getColor()<<endl;
	cout <<"Dog weight: "<<dog.getWeight()<<endl;
    
	cout <<"BYE";

	cin.get();


	return 0;




}

Library.h

Code:

//Lib
#include <windows.h>
#include <fstream>
#include <iostream>
#include <string>

using namespace std;

//Headers
#include "Dog.h"

Dog.cpp

Code:

#include "Library.h"


//Dog name

string Dog::getName()
{
	return name;
}

void Dog::setName(string dogname)
{
	name = dogname;

}

//Dog Weight

int Dog::getWeight()
{
	return weight;
}

void Dog::setWeight(int dogweight)
{

	weight = dogweight;
}

//Dog Color

string Dog::getColor()
{
	return color;
}

void Dog::setColor(string dogcolor)
{
	color = dogcolor;

}

//Destructor/Constructor

Dog::Dog()
{

}

Dog::~Dog()
{

}

//reset

int Dog::reset()
{
	name = "";
	color = "";
	weight = NULL;
	return true;
}

Dog.h

Code:

//Dog class


class Dog
{

public:

	 Dog();
	~Dog();

	//Name
	string getName();
	void setName(string dogname);
	//Weight
	int getWeight();
	void setWeight(int dogweight);
	//Color
	string getColor();
	void setColor(string dogcolor);

        //reset data
	int reset(); 


private:
	string name;
	int weight;
	string color;
    

};

This will create the dog, and finish by destroying it. You may compile it and check it. Now, when you checked it. There's a bug huh? It doesnt destroy the weight of the dog. Now, in the destructor, i have decided to put weight = 0;. But, it will show Dog weight: 0 on the screen. I want it to just destroy it forever and don't show it. Can anyone help me. Thank you.

Code:

	dog.~Dog();
	system("cls");

	cout <<"Let's check if your dog has been destroyed.Press enter again."<<endl;
	cin.get();

	cout <<"Dog name: "<<dog.getName()<<endl;
	cout <<"Dog color: "<<dog.getColor()<<endl;
	cout <<"Dog weight: "<<dog.getWeight()<<endl;

I wish that were a syntax error, instead of just undefined behavior. But alas, it's only undefined behavior. Referring to dog after it has been destroyed can't possibly give you anything valid; since you haven't done anything to reuse the memory the old contents are still there.

Well, it's supposed to destroy the weight, the name, the color and set them to null...since the dog class still exist. But, it doesn't look like it does that. it actually set the name and the color to NULL, but not the weight.

Originally Posted by kevinawad

Well, it's supposed to destroy the weight, the name, the color and set them to null...since the dog class still exist. But, it doesn't look like it does that. it actually set the name and the color to NULL, but not the weight.

It doesn't on my system -- the name and the color are still printed after destruction.

That's the point. The compiler is allowed to do whatever it wants in this situation -- it could play the theme song to "Cheers" through the speakers if it wanted -- because it's not a legal thing to access dog after it's been destroyed.

>> There's a bug huh? It doesnt destroy the weight of the dog. Now, in the destructor, i have decided to put weight = 0;. But, it will show Dog weight: 0 on the screen. I want it to just destroy it forever and don't show it. Can anyone help me. Thank you.

first of all, you should *never* explicitly call a destructor (there are exceptions, but they are few and rare). it's generally the compiler's job to do that when the variable goes out of scope. furthermore, once the destructor has been called you *must never* attempt to access the variable's data members in any way (remember: it is effectively 'destroyed'/nonexistant at that point). but to answer your question, it is simply that POD's (Plain Old DataTypes) such as ints don't have a destructor...

Oh, hmm...ill try something else to destroy all the data in dog then.

Next, try making an abstract class Animal from which you can derive your Dog

Originally Posted by kevinawad

Oh, hmm...ill try something else to destroy all the data in dog then.

Why would you *want* to destroy all the data in dog then? If you don't want the dog variable at all, or you want the dog variable later to have no relation to the dog variable earlier, then use the scope rules (via judicious use of curly brackets) to make sure the variable is gone.

If your class design requires you for whatever reason to "clean out" a variable, then you should make a reset method.

Here. put this in the Dog class in Dog.h.(public)

Code:

int reset();

This in Dog.cpp

Code:

int Dog::reset()
{
	name = "";
	color = "";
	weight = NULL;
	return true;
}

Replace dog.~Dog() to dog.reset(); in main.cpp


Now, it should reset but, it will print weight as 0;
How is it possible to set an integer to null?

isn't zero good enough? anyway, you can simply store a boolean flag to indicate that the data is valid if you're that concerned about it.

Well, NULL == 0. It is defined as such in the C++ standard.

And, let me put this in boldface this time: IF the variable dog exists, then the variable dog.weight WILL exist. All the member variables will exist. The only way to get rid of weight is to get rid of dog, and the only way to get rid of dog is to let it go out of scope.

Let's get rid of classes, since they seem to have gotten in the way, and look at this:

Code:

int foo = 3;

How do you propose to set foo to NULL?

What do you mean sebastiani? could you show me a little example? Thank you.


Hmm...isn't there any way to just set it to nothing? like delete the zero?

Every variable has a value, even if it's bogus (like what you get when you try to access invalid memory).
There's no way to explicitly delete memory allocated on the stack, and assigning "null" doesn't do much except let you check, later on, whether the memory is valid, which usually only applies to pointers.


(In response to below):

Originally Posted by rudyman

Next, try making an abstract class Animal from which you can derive your Dog

Weight = 0 is okay, i'm not doing that to make a big program, it's just my project for classes. i done it now, now, i am comfortable with classes and know how they work...now, i can work on something else. That's what im going to do right now.

I think you need to change how you're approaching this. Your thinking is off. What you're trying to do might work better in Java. In C++, a local object exists until the end of the block it was declared in. As was mentioned, if you want an object to not exist any more, then make sure it is in a block that ends when you don't need it.

In some cases the lifetime of the object won't fit neatly into a block and you can use dynamic memory. But those cases are much rarer than you think.