Top 50 C++ Interview Questions for Freshers

Welcome to this comprehensive guide on the top C++ interview questions tailored for freshers. Each question comes with a collapsible section where you can view the answer by clicking.

Below is the curated list of frequently asked C++ interview questions:

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Questions

1. What is C++?

C++ is a general-purpose programming language created by Bjarne Stroustrup in the early 1980s at Bell Labs. Initially, it was called "C with Classes" as it was designed as an extension to the C programming language. The goal was to add object-oriented features, such as classes and objects, to C, which was primarily procedural.

C++ was influenced by several other programming languages, including Simula, which was one of the first languages to support object-oriented programming (OOP), and Algol, which influenced its syntax. The combination of these ideas with the power and efficiency of C resulted in a language that was both flexible and efficient for system and application programming.

C++ brought forward the concept of objects, encapsulation, inheritance, and polymorphism. It also introduced generic programming with the addition of templates and low-level memory manipulation using pointers, making it suitable for both system-level programming and high-performance applications.

C++ has since evolved into one of the most popular programming languages in the world, widely used in various fields, including game development, systems programming, and high-performance applications.

Example:

#include <iostream>
using namespace std;

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

This program demonstrates a simple "Hello, World!" program in C++.

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

The main features of C++ include:

• Object-Oriented Programming (OOP)
• Encapsulation
• Inheritance
• Polymorphism
• Abstraction
• Generic Programming
• Operator Overloading
• Exception Handling

Example:

#include <iostream>
using namespace std;

class Example {
    int value;
  public:
    void setValue(int v) { value = v; }
    int getValue() { return value; }
};

int main() {
    Example ex;
    ex.setValue(42);
    cout << "Value: " << ex.getValue() << endl;
    return 0;
}

This demonstrates encapsulation, a key feature of C++.

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3. How is C++ different from C?

C++ is often referred to as an extension of the C programming language, but it introduces significant enhancements that elevate it beyond C's procedural roots. While C is a purely procedural language, C++ combines procedural programming with object-oriented and generic programming paradigms, giving developers more powerful tools for managing complex systems and enhancing code maintainability.

The development of C++ arose due to the limitations in C that hindered scalability, maintainability, and code organization in large and complex systems. Here’s a detailed comparison of how C++ addresses these gaps:

What C Lacked, Leading to C++:

1. Lack of Object-Oriented Programming (OOP) Support:

   • C: C is a procedural language, meaning it lacks the concept of objects, classes, inheritance, polymorphism, and encapsulation. As a result, C code can quickly become difficult to maintain and scale, especially in larger projects.
   • C++: C++ introduces Object-Oriented Programming (OOP) features, including classes and objects, which make it easier to organize and maintain complex systems by modeling real-world entities and their interactions.

2. Inflexible Memory Management:

   • C: In C, memory management is manual and prone to errors, using functions like malloc() and free(). Memory leaks and pointer errors are common pitfalls.
   • C++: C++ enhances memory management by providing automatic memory management through constructors and destructors and supports RAII (Resource Acquisition Is Initialization), allowing developers to better manage resources like memory, file handles, and network connections.

3. No Support for Function and Operator Overloading:

   • C: In C, functions and operators must have unique names and cannot be overloaded to handle different types or numbers of arguments.
   • C++: C++ supports function overloading and operator overloading, which allows the same function or operator to be used with different parameter types or for user-defined types, making the code more intuitive and reducing redundancy.

4. No Template Programming:

   • C: C lacks the ability to define functions or classes that work with any data type. This results in repetitive code and a lack of flexibility.
   • C++: C++ introduces templates, enabling generic programming. With templates, developers can write functions or classes that work with any data type without duplicating code, improving code reuse and flexibility.

5. No Exception Handling:

   • C: In C, error handling is often done through return codes or global error flags, which can be cumbersome and error-prone.
   • C++: C++ introduces exception handling using try, catch, and throw, which provides a more structured way to handle errors, separating error-handling code from normal program logic.

6. Lack of Namespaces:

   • C: C lacks the concept of namespaces, which means that when multiple libraries are used in a program, symbol conflicts (name clashes) can occur, especially in large projects.
   • C++: C++ introduces namespaces, which prevent name collisions by grouping related code into separate namespaces, thus promoting modular programming.

7. Limited Standard Library:

   • C: C’s standard library is limited in terms of data structures and algorithms. Developers must often implement their own versions of common data structures like linked lists, stacks, and queues.
   • C++: C++ provides an extensive Standard Template Library (STL), which includes pre-implemented data structures (such as vectors, lists, maps, and sets) and algorithms (such as sort, search, and transform). This dramatically reduces the amount of code developers need to write and improves productivity.

Here’s a detailed comparison between the two languages:

Feature	C	C++
Programming Paradigm	Procedural	Procedural + Object-Oriented
Extension	None	Extension of C
Encapsulation	Not Supported	Supported
Inheritance	Not Supported	Supported
Polymorphism	Not Supported	Supported
Exception Handling	Not Supported	Supported
Standard Libraries	Limited	Extensive

Example: In C:

#include <stdio.h>

int main() {
    printf("Hello, C!
");
    return 0;
}

In C++:

#include <iostream>
using namespace std;

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

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4. What are the different data types in C++?

The primary data types in C++ are:

• int
• float
• double
• char
• bool

In addition, C++ also supports user-defined types like classes and enums, as well as derived types such as arrays, pointers, and references.

Example:

#include <iostream>
using namespace std;

int main() {
    int age = 25;
    float height = 5.9;
    char grade = 'A';
    bool isPassed = true;

    cout << "Age: " << age << ", Height: " << height << ", Grade: " << grade << ", Passed: " << isPassed << endl;
    return 0;
}

This demonstrates various basic data types in C++.

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5. Explain the concept of Object-Oriented Programming (OOP).

OOP is a programming paradigm based on objects which can contain data and methods. The core concepts of OOP include:

• Encapsulation
• Inheritance
• Polymorphism
• Abstraction

Example:

#include <iostream>
using namespace std;

class Animal {
  public:
    void sound() { cout << "Animals make sounds" << endl; }
};

class Dog : public Animal {
  public:
    void sound() { cout << "Dogs bark" << endl; }
};

int main() {
    Dog dog;
    dog.sound();
    return 0;
}

This example demonstrates inheritance and polymorphism.

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6. What is the difference between a class and an object?

• A class is a blueprint or prototype for creating objects.
• An object is an instance of a class, containing actual data and behaviors defined by the class.

Example:

#include <iostream>
using namespace std;

class Car {
  public:
    string brand;
    void honk() { cout << brand << " says Beep!" << endl; }
};

int main() {
    Car car1;
    car1.brand = "Toyota";
    car1.honk();
    return 0;
}

This program shows how a class is used to create an object.

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7. What is inheritance in C++?

Inheritance is a feature of OOP in which one class (derived class) inherits properties and behaviors from another class (base class), promoting code reuse and hierarchy design.

Example:

#include <iostream>
using namespace std;

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

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

int main() {
    Child obj;
    obj.show();
    obj.display();
    return 0;
}

This demonstrates simple inheritance.

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8. What is a constructor in C++?

A constructor is a special member function of a class that initializes objects. It has the same name as the class and no return type.

Example:

#include <iostream>
using namespace std;

class Person {
  public:
    string name;
    Person(string n) { name = n; }
    void display() { cout << "Name: " << name << endl; }
};

int main() {
    Person p("Alice");
    p.display();
    return 0;
}

This demonstrates the use of a constructor.

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9. What is a destructor in C++?

A destructor is a special member function of a class that is executed when an object goes out of scope or is explicitly deleted. It has the same name as the class, preceded by a tilde (~).

Example:

#include <iostream>
using namespace std;

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

int main() {
    Demo d;
    return 0;
}

This demonstrates the invocation of a destructor.

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10. What is function overloading in C++?

Function overloading allows multiple functions with the same name but different parameter lists to exist in the same scope. It enables the same function name to handle different types or numbers of arguments.

Example:

#include <iostream>
using namespace std;

class Calculator {
  public:
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }
};

int main() {
    Calculator calc;
    cout << "Sum (int): " << calc.add(3, 4) << endl;
    cout << "Sum (double): " << calc.add(2.5, 4.5) << endl;
    return 0;
}

This demonstrates function overloading.

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Stay tuned for the remaining questions and answers!