Thread: classes are pain

i know i've started aot of threads recently but i really want to learn c++. classes are killing me. my tutorial just isn't doing me anygood. its been great till now though look at it, ill put in comments where im having trouble

Code:

#include <iostream>
using namespace std;

class Dog {
private:
    int age;
    int weight;
public:
    Dog();      //Constructor?how and why does it work?
    ~Dog();    //Destructor?"                                     "
    void setAge(int age);//whats with void? what is it, how does it
//work? and o this is killing me, please just explain every line of code. i know its alot to ask but ill give you drugs for it(joking)
    int getAge();
    void setWeight(int weight);
    int getWeight();
    void speak();
};

Dog::Dog()
{
    age = 0;
    weight = 0;
    cout << "Dog Constructor Called" << endl;
}

Dog::~Dog()
{
    cout << "Dog Destructor Called" << endl;
}

void Dog::setAge(int age)
{
    this->age = age;
}

int Dog::getAge()
{
    return age;
}

void Dog::setWeight(int weight)
{
    this->weight = weight;
}

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

void Dog::speak()
{
    cout << "BARK!!" << endl;
}

int main()
{
    Dog fido;
    Dog rover;

    cout << "Rover is " << rover.getAge() << " years old." << endl;
    cout << "He weighs " << rover.getWeight() << " lbs." << endl;
    cout << endl;

    cout << "Updating Rover's Age and Weight" << endl;
    rover.setAge(1);
    rover.setWeight(10);

    cout << "Rover is " << rover.getAge() << " years old." << endl;
    cout << "He weighs " << rover.getWeight() << " lbs." << endl;
    cout << endl;

    cout << "Fido is " << fido.getAge() << " years old." << endl;
    cout << "He weighs " << fido.getWeight() << " lbs." << endl;

    cout << "Setting Fido to be the same as Rover" << endl;
    fido = rover;

    cout << "Fido is " << fido.getAge() << " years old." << endl;
    cout << "He weighs " << fido.getWeight() << " lbs." << endl;

    rover.speak();
    fido.speak();
    
    cin.get();

    return 0;
}

A generally better way of initializing variables in the constructor is the initialization list. It doesn't matter so much for ints, but for more complex data types it is required or just more efficient:

Code:

Dog::Dog() : age(0), weight(0)
{
    cout << "Dog Constructor Called" << endl;
}

Originally Posted by axon

destructor: not used very widely anymore, but it is used for clean up when the object is deleted; lets say you dynamically allocate memory somewhere in you class, one place that you could deallocate it is inside the destructor.

? Not used very widely anymore ? The destructor is actually very usefull. Besides cleaning up resources like dynamically allocated memory, it is used with RAII in designing exception safe code, one example being a smart pointer. Another example is an fstream object. When the fstream goes out of scope, the file is closed automatically, so you don't have to worry about closing the file if there are exceptions or if you just want to return early from your function. The destructor takes care of it for you.

destructor: not used very widely anymore

Uh buddy hate to tell you but the destructor is used on every object that is created. Now if you want to say that they aren't written by the user much any more then thats ok

If you're having trouble understanding classes, go back and make sure you understand structures. Structures are like classes without functions. (Technically, structures can have functions in C++.)

whats with void?

Void means that the function doesn't return a value. Go back and re-study functions! Everything in C++ is done with functions, and if you don't understand functions, you should not be trying to understand classes & objects yet.

void setAge(int age); // This is an accessor function. It allows you to "get to" the private variable age.

The constructor creates an object in the computer's memory and initializes it. You can't call fido.SetAge() if fido hasn't been constructed.