Class, Object, And Method



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

class MyClass
{
public:
    int num;
    string Str;

    // Method

    void method()
    {
        // Method--> function  inside A class
        cout << "Hello This is Method";
    }
};

int main()
{
    MyClass Obj;
    Obj.num = 50;
    Obj.Str = "This is Str\n";

    cout << Obj.num << "\n";
    cout << Obj.Str;
    Obj.method();
    return 0;
}


output


50
This is Str
Hello This is Method


Constructors and Access Specifiers


public - members are accessible from outside the class
private - members cannot be accessed (or viewed) from outside the class
protected - members cannot be accessed from outside the class, however, they can be accessed in inherited classes. You will learn more about Inheritance later.



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

class Person
{
public: // Public access specifier
    int x;

private: // Private access specifier
    int y;
};

int main()
{
    Person Obj;
    Obj.x = 100;
    Obj.y = 150; // Not access
    return 0;
}


////////


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

class Person
{ // The class
public:
    string firstName;
    string lastName;
    int age;
    // Constructor
    Person(string x, string y, int z)
    {
        firstName = x;
        lastName = y;
        age = z;
    }
};

int main()
{

    Person Obj1("Rezaul", "Karim", 22);
    cout << Obj1.firstName << " " << Obj1.lastName << " "
<< carObj1.age << "\n";

    return 0;
}

output


Rezaul Karim 22


Encapsulation



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

class Person
{
private:
    string name;

public:
    // void
    void SetName(string x)
    {
        name = x;
    }
    string GetName()
    {
        return name;
    }
};

int main()
{

    Person Obj;
    Obj.SetName("Rezaul Karim");
    cout << Obj.GetName();

    return 0;
}

output


Rezaul Karim


Inheritance





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

// Person class
class Person
{

public:
    string name;
    int age;

    // input function
    void input()
    {
        cout << "Enter Your Name : ";
        cin >> name;
        cout << "Enter Your age : ";
        cin >> age;
    }
    // display function
    void display()
    {
        cout << "Name : " << name << endl;
        cout << "age : " << age << endl;
    }
};
// Student class
class Student : public Person // Student class inheritance Person class
{

public:
    int roll;

    // StudentInput function
    void studentInput()
    {
        input(); // input function from Person class
        cout << "Enter Your Roll : ";
        cin >> roll;
    }
    // display function
    void studentDisplay()
    {
        display(); // display function from Person class
        cout << "Roll : " << roll << endl;
    }
};

int main()
{
    Student obj;
    obj.studentInput();
    obj.studentDisplay();

    return 0;
}



output


Enter Your Name : rezaul
Enter Your age : 22
Enter Your Roll : 50

Name : rezaul
age : 22
Roll : 50




Polymorphism



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

// Base class
class Person
{
public:
    void personFunction()
    {
        cout << "This is person Function \n";
    }
};

// Derived class
class Student : public Person
{
public:
    void personFunction()
    {
        cout << "This is person Function From Student class\n";
    }
};

// Derived class
class Student2 : public Person
{
public:
    void personFunction()
    {
        cout << "This is person Function From Student2 class\n";
    }
};

int main()
{
    Person PersonDisplay;
    Student StudentDisplay;
    Student2 Student2Display;

    PersonDisplay.personFunction();
    StudentDisplay.personFunction();
    Student2Display.personFunction();
    return 0;
}


output


This is person Function
This is person Function From Student class
This is person Function From Student2 class



Abstraction 



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

class Person
{
private:
    string name;
    int age; // private variables
public:
    void input()
    {
        cout << "Enter name: ";
        cin >> name;
        cout << "Enter age: ";
        cin >> age;
    }
    void display()
    {
        cout << "Name is : " << name << "\n Age is : " << age << endl;
    }
};
int main()
{
    Person obj;
    obj.input();
    obj.display();
    return 0;
}


output


Enter name: reza
Enter age: 22

Name is : reza
Age is : 22


Files


ofstream --- Creates and writes to files
ifstream ---  Reads from files
fstream --  A combination of ofstream and ifstream: creates, reads, and writes to files




#include <iostream>
#include <fstream>
using namespace std;

// Create and open a text file
int main()
{

    string name;
    ofstream file("Student.txt", ios::out | ios::app);

    cout << "Enter Your Name : ";
    getline(cin, name);

    file << "welcome " << name << endl;
    file.close();
    return 0;
}

// Read text file
int main()
{

    string line;
    ifstream file("Student.txt", ios::out | ios::app);

    while (getline(file, line))
    {
        cout << line << endl;
    }

    file.close();
    return 0;
}