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If you’re preparing for a C++ interview, this guide will help you understand the most common questions with easy explanations and examples. These are simple, beginner-friendly answers — written like how a human would explain in a real interview.

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1. What is C++?

Answer:
C++ is an object-oriented programming language created by Bjarne Stroustrup. It is an extension of the C language with added features like classes, objects, inheritance, polymorphism, and encapsulation.
It is widely used for system software, game development, and competitive programming.

Example:

#include <iostream>
using namespace std;

int main() {
    cout << "Hello, C++!" << endl;
    return 0;
}

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2. What are the main features of C++?

Answer:
Some of the important features of C++ are:

• Object-Oriented Programming (OOP)
• Platform Independence
• High Performance
• Reusability through Inheritance
• Function Overloading and Operator Overloading
• Rich Library Support

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3. What is the difference between C and C++?

Feature	C	C++
Type	Procedural	Object-Oriented
Focus	Functions	Objects & Classes
Data Security	Less (No encapsulation)	More (Encapsulation & Abstraction)
Overloading	Not supported	Supported
Inheritance	Not supported	Supported

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4. What are classes and objects in C++?

Answer:
A class is a blueprint for creating objects. An object is an instance of a class that contains real values.

Example:

#include <iostream>
using namespace std;

class Student {
public:
    string name;
    int age;
    void display() {
        cout << "Name: " << name << ", Age: " << age << endl;
    }
};

int main() {
    Student s1;
    s1.name = "Riya";
    s1.age = 21;
    s1.display();
}

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5. What is the difference between a constructor and a destructor?

Answer:

• Constructor: Automatically called when an object is created.
• Destructor: Automatically called when an object is destroyed.

Example:

#include <iostream>
using namespace std;

class Demo {
public:
    Demo() { cout << "Constructor called" << endl; }
    ~Demo() { cout << "Destructor called" << endl; }
};

int main() {
    Demo obj;
}

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6. What is inheritance in C++?

Answer:
Inheritance allows one class to acquire the properties and methods of another class. It helps in reusing existing code.

Example:

#include <iostream>
using namespace std;

class Parent {
public:
    void show() { cout << "This is Parent class" << endl; }
};

class Child : public Parent {
public:
    void display() { cout << "This is Child class" << endl; }
};

int main() {
    Child obj;
    obj.show();
    obj.display();
}

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7. What is polymorphism?

Answer:
Polymorphism means “many forms”. It allows one function to behave differently based on the object that calls it.
There are two types:

1. Compile-time Polymorphism (Static) — using function overloading or operator overloading.
2. Run-time Polymorphism (Dynamic) — using virtual functions.

Example:

#include <iostream>
using namespace std;

class Shape {
public:
    virtual void draw() { cout << "Drawing Shape" << endl; }
};

class Circle : public Shape {
public:
    void draw() override { cout << "Drawing Circle" << endl; }
};

int main() {
    Shape* s = new Circle();
    s->draw();
    delete s;
}

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8. What is encapsulation?

Answer:
Encapsulation means wrapping data and methods together in a single unit. It helps protect data from unauthorized access.

Example:

class Account {
private:
    double balance;

public:
    void setBalance(double b) { balance = b; }
    double getBalance() { return balance; }
};

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9. What are access specifiers in C++?

Answer:
Access specifiers define how class members can be accessed.

• Public: Accessible from anywhere.
• Private: Accessible only inside the class.
• Protected: Accessible in the class and derived classes.

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10. What is the difference between compile-time and run-time polymorphism?

Type	Description	Example
Compile-time	Resolved during compilation	Function overloading
Run-time	Resolved during execution	Virtual functions

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11. What is a virtual function in C++?

Answer:
A virtual function is a function in the base class that can be overridden in the derived class. It allows run-time polymorphism.

Syntax:

virtual void functionName();

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12. What is the use of ‘this’ pointer in C++?

Answer:
this pointer refers to the current object of the class. It helps to distinguish between class variables and parameters when they have the same name.

Example:

class Demo {
    int x;
public:
    Demo(int x) {
        this->x = x;
    }
};

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13. What is a copy constructor?

Answer:
A copy constructor initializes a new object as a copy of an existing object.

Example:

class Test {
public:
    int a;
    Test(int x) { a = x; }
    Test(const Test &t) { a = t.a; }  // Copy constructor
};

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14. What is function overloading?

Answer:
Function overloading allows multiple functions with the same name but different parameter lists.

Example:

int add(int a, int b) { return a + b; }
double add(double a, double b) { return a + b; }

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15. What is operator overloading?

Answer:
Operator overloading allows us to redefine operators for user-defined data types.

Example:

class Complex {
public:
    int real, imag;
    Complex operator + (Complex obj) {
        Complex temp;
        temp.real = real + obj.real;
        temp.imag = imag + obj.imag;
        return temp;
    }
};

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16. What is the difference between struct and class in C++?

Feature	struct	class
Default Access	public	private
Inheritance	Supported	Supported
Object-Oriented	Not fully	Fully

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17. What is the use of a namespace in C++?

Answer:
Namespace helps avoid name conflicts by grouping related identifiers under one name.

Example:

namespace MyNamespace {
    int x = 100;
}

int main() {
    cout << MyNamespace::x;
}

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18. What are templates in C++?

Answer:
Templates allow writing generic programs that work with any data type.

Example:

template <typename T>
T add(T a, T b) {
    return a + b;
}

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19. What is an exception in C++?

Answer:
An exception is an event that occurs during program execution that disrupts the flow.
C++ handles exceptions using try, catch, and throw blocks.

Example:

try {
    int x = 5, y = 0;
    if (y == 0) throw "Division by zero!";
}
catch (const char* msg) {
    cout << msg;
}

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20. What is the difference between malloc() and new in C++?

Feature	malloc()	new
Syntax	C-style	C++ operator
Returns	void pointer	Exact data type
Calls constructor	No	Yes

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21. What is STL in C++?

Answer:
STL (Standard Template Library) is a collection of templates for data structures and algorithms like vectors, stacks, queues, maps, and sets.

Example:

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

int main() {
    vector<int> v = {1, 2, 3};
    v.push_back(4);
    for (int i : v)
        cout << i << " ";
}

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✅ Final Tips for Freshers

• Focus on basic concepts (OOP, inheritance, polymorphism, templates).
• Practice writing small programs daily.
• Understand memory management (pointers, new, delete).
• Revise STL and exception handling.

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