Most asking CPP

Note : Basics

The latest official C++ standard is C++23.

It was developed by Bjarne Stroustrup in 1985.

• #include <iostream> → used for input/output

• using namespace std → allows using standard functions for remove space

• main() → starting point of program

• cout → prints output

• cin → Take input from user

• endl → Line Break

• return 0 → program ends successfully

cout is pronounced "see-out". Used for output, and uses the insertion operator (<<)

cin is pronounced "see-in". Used for input, and uses the extraction operator (>>)

What is C++?

• C++ most popular Object Orineted Programming Language (OOPs)

• C++ was developed as an extension of C

• Supports classes and objects

• C++ is used for system software and games

What are the main features of C++?

Main features are:

• Object-Oriented Programming

• Classes and Objects

• Inheritance

• Polymorphism

• Encapsulation

• Data Abstraction

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What is a Constructor?

A constructor is a special function that is automatically called when an object is created.

• Same name as class

• Constructor doesn't have any return type

• Only called onece (automatically), Object creaction

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What is a Destructor?

A destructor is a special function that is automatically called when an object is destroyed.

• It is mainly used to free memory or clean up resources.

• Example: Closing files, releasing memory, deleting pointers.

• Destructor name is the same as the class name

• It has a tilde (~) before the name

#include <iostream>
using namespace std;

class Test {
public:
 Test() {
 cout << "Constructor called" << endl;
 }

 ~Test() {
 cout << "Destructor called" << endl;
 }
};

int main() {
 Test obj;
}

• It has no return type

• It takes no parameters

• It is called automatically

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What is a Pointer?

A pointer is a variable that stores the memory address of another variable. Instead of storing a value, it stores where the value is located in memory.

int *ptr; //This means ptr is a pointer that can store the address of an integer variable.

• Dynamic memory allocation

• Passing arguments to functions

• Working with arrays

• Efficient memory use

#include <iostream>
using namespace std;

int main() {
 int a = 10;
 int *ptr;

 ptr = &a;

 cout << "Value of a: " << a << endl;
 cout << "Address of a: " << &a << endl;
 cout << "Pointer value (address): " << ptr << endl;
 cout << "Value using pointer: " << *ptr << endl;

 return 0;
}

Code Meaning

• int a = 10;Create variable a

• int *ptr;Create pointer to integer

• ptr = &a;Store address of a in ptr

• &aAddress of variable a

• *ptrValue stored at that address

5️⃣ Important Symbols

• &Address-of operator

• *Pointer / Dereference operator

Difference between C and C++

• C is a procedural language focused on functions.

• C++ is an object-oriented language focused on classes and objects.

Access Specifiers

Access specifiers in C++ are used to control the accessibility (visibility) of class members such as variables and functions.

They help in data hiding and security of a program.

There are three main types of access specifiers:

1. Public - Members declared as public can be accessed from anywhere in the program.

   #include <iostream>
   using namespace std;
   
   class Student {
   public:
    int age;
   
    void show() {
    cout << age;
    }
   };
   
   int main() {
    Student s;
    s.age = 20;
    s.show();
   }

   • Accessible inside the class

   • Accessible outside the class

   • Accessible by derived (child) classes

   • Mostly used for functions that interact with objects

2. Protected - Members declared as protected can be accessed inside the class and by derived (child) classes, but not outside the class.

   class Parent {
   protected:
    int value;
   };
   
   class Child : public Parent {
   public:
    void setValue() {
    value = 10;
    }
   };

   • Accessible inside the class

   • Accessible in derived classes (inheritance)

   • Not accessible outside the class

   • Mainly used in inheritance

3. Private - Members declared as private can be accessed only inside the class.

   class Demo {
   private:
    int num;
   
   public:
    void setNum() {
    num = 5;
    }
   };

   • Accessible inside the class only

   • Not accessible outside the class

   • Not accessible in derived classes

   • Used for data hiding

   

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