Classes_and_Objects.md

Classes and Objects

Classes

• Blueprints from which objects are created
• user friendly data type
• has attributes, methods..
• provide a public interface

Classes should be named so that "object.function" is easy to read and appears to be logical.

class NiceClass{
public:    
    string niceString{};
    int niceInt{};
};

Objects

• Created from classes
• represents a specific instance of a class
• can create many objects
• has its own identity
• each can use the defined class methods

class NiceClass{
public:

    string niceString{};
    int niceInt{};
};

int main(){
    NiceClass niceObject;
    niceObject.niceString = "The nice string";
    cout<<niceObject.niceString;
}

Class members modifiers

• Public

Accessible everywhere

• Private

accessible only for members of the class

• Protected

Used in inherence

Constructors

#include<iostream>
#include <bits/stdc++.h>
using namespace std;

class NiceClass{
public:
    string niceString{};
    int niceInt{};
    NiceClass(string nicestring, int niceint){ //constructor
        niceString = nicestring;
        niceInt = niceint;
    }
};

int main(){

    NiceClass niceObject("The nice string", 1);

    cout<<niceObject.niceString<<" "<<niceObject.niceInt;
    return 0;
}

The header .h file holds the function declarations (prototype) and variables declarations:

// in NiceClass.h
#ifndef NICECLASS_H
#define NICECLASS_H
#include<iostream>
using namespace std;

class NiceClass
{

public:
    string niceString;
    int niceInt;
    NiceClass(string nicestring, int niceint);
    string msg();
};

#endif // NICECLASS_H

Models - Implementation and methods go in the source ".cpp" file ("::" is called binary scope resolution operator):

//in NiceClass.cpp
#include "NiceClass.h"

NiceClass::NiceClass(string nicestring,int niceint)

{
    niceString = nicestring;
    niceInt = niceint;

}

string NiceClass::msg()
{
    cout<<niceString<<" "<<niceInt<<endl;
}

And main then:

//main.cpp
#include<iostream>
#include <bits/stdc++.h>
#include<NiceClass.h>
using namespace std;

//class NiceClass{
//public:
//    string niceString{};
//    int niceInt{};
//    NiceClass(string nicestring, int niceint){
//        niceString = nicestring;
//        niceInt = niceint;
//    }
//};

int main(){

    NiceClass niceObject("The nice string", 1);
    niceObject.msg();

    //cout<<niceObject.niceString<<" "<<niceObject.niceInt;
    
    return 0;
}

Declarations always go in the header files and implementation go in the source files (.cpp), if any methods, these methods should go outside the curly brackets where the other variables are..