Introduction
C++ – the must-known and all-time favorite programming language of coders. It is still as relevant today as it was in the mid-80s. As a general-purpose and object-oriented programming language, C++ is extensively employed in a wide range of applications, from system programming to game development. Top IT companies like Microsoft, Google, Amazon, and Meta heavily rely on C++ for its performance, reliability, and versatility.
To get hired at these leading tech firms, you need to be well-versed in C++ and demonstrate a deep understanding of the language‘s core concepts and advanced features. In this comprehensive guide, we‘ll cover the top 50 C++ interview questions that can help you ace your upcoming interviews and showcase your expertise as a C++ programmer.
About the Author
My name is [Your Name], and I am a seasoned programming and coding expert with over [X] years of experience in the industry. I have a deep passion for C++ and have been using it extensively in my work, ranging from developing high-performance systems to building complex, scalable applications.
Throughout my career, I have had the opportunity to interview numerous candidates for C++ programming roles at various tech companies. This hands-on experience has given me a unique perspective on the key skills and knowledge that employers are looking for in C++ developers. I am excited to share my insights and help you prepare for your next C++ interview.
C++ Interview Questions for Freshers
1. What is C++? What are the advantages of C++?
C++ is an object-oriented programming language that was introduced to overcome the limitations of the C programming language. It supports features like polymorphism, inheritance, abstraction, and encapsulation, making it a powerful tool for building complex, scalable, and efficient applications.
Some of the key advantages of C++ include:
Object-Oriented Programming (OOP): C++ is an OOP language, which means the data is organized into objects with their own properties and behaviors. This allows for better code organization, modularity, and reusability.
Multi-Paradigm: C++ supports multiple programming paradigms, including procedural, functional, and object-oriented, allowing developers to choose the best approach for their specific needs. This flexibility makes C++ a versatile language that can be used in a wide range of applications.
Memory Management: C++ provides low-level control over memory management, enabling dynamic memory allocation and deallocation, which is crucial for developing system-level software and high-performance applications. This level of control can be both a blessing and a curse, as it requires developers to be more mindful of memory usage and potential memory leaks.
Performance: C++ is a compiled language, which means it can generate highly optimized machine code, making it one of the fastest programming languages available. This performance advantage is particularly important for applications that require real-time processing or low-level system interactions.
Portability: C++ code can be compiled and executed on a wide range of platforms, from embedded systems to high-performance servers, making it a versatile choice for cross-platform development. This portability is achieved through the use of standardized libraries and the ability to write platform-specific code when necessary.
2. What are the different data types present in C++?
C++ supports a wide range of data types, including:
- Fundamental Data Types:
int,float,double,char,bool,void - Derived Data Types:
array,pointer,reference,function - User-Defined Data Types:
struct,union,enum,class
Each data type has its own range of values and memory requirements, which is important to consider when writing efficient and robust C++ code. Choosing the appropriate data type for a particular use case can have a significant impact on the performance and memory usage of your application.
3. Define ‘std‘?
The std keyword in C++ refers to the "standard" namespace, which is part of the C++ Standard Library. The std namespace contains a wide range of pre-defined functions, classes, and objects that are commonly used in C++ programming, such as cout, cin, string, and vector.
By using the using namespace std; directive, you can avoid having to prefix every standard library element with the std:: scope resolution operator, making your code more concise and readable. However, it‘s generally considered a best practice to use the std:: prefix explicitly to avoid potential naming conflicts with user-defined identifiers.
4. What are references in C++?
In C++, a reference is an alternative way to create an alias for another variable. A reference acts as a synonym for a variable, allowing you to access the variable directly without any additional syntax. References must be initialized when created and cannot be changed to refer to another variable afterward.
Syntax:
int GFG = 10; // reference variable
int& ref = GFG;References are particularly useful when working with functions, as they allow you to pass variables by reference, enabling the function to modify the original values directly. This can be more efficient than passing large objects by value, which involves creating a copy of the object.
5. What do you mean by Call by Value and Call by Reference?
In C++, there are two methods for calling a function:
- Call by Value: A copy of the variable is passed to the function. Changes made to the function parameters do not affect the original variables.
- Call by Reference: The variable itself is passed to the function. Changes made in the function can be seen outside the function and affect the original variables.
The key differences are:
| Call by Value | Call by Reference |
|---|---|
| A copy of a variable is passed. | The variable itself is passed. |
| Changes made in the function are not reflected outside the function. | Changes made in the function can be seen outside the function. |
| Passed actual and formal parameters are stored in different memory locations. | Passed actual and formal parameters are stored in the same memory location. |
Call by reference is generally more efficient, as it avoids the overhead of creating and copying objects. However, it also requires more care to ensure that the function doesn‘t accidentally modify the original variables in unintended ways.
6. Define token in C++
In C++, a token is the smallest individual element of a program that is understood by the compiler. Tokens can be classified into the following categories:
- Keywords: Special words that have a predefined meaning in the language, such as
int,class,if, etc. - Identifiers: Names used to identify variables, functions, classes, etc.
- Constants: Values that do not change throughout the program‘s execution.
- Strings: Sequences of characters enclosed within double quotes.
- Special Symbols: Symbols like
[],(),{},;,*,=, etc., which have special meaning in the language. - Operators: Symbols that perform operations on operands, such as
+,-,*,/, etc.
Understanding the different types of tokens and their roles in C++ syntax is crucial for writing correct and maintainable code.
7. What is the difference between C and C++?
The key differences between C and C++ are:
| C | C++ |
|---|---|
| Procedural programming language | Mixture of procedural and object-oriented programming language |
| Does not support OOP concepts like polymorphism, data abstraction, encapsulation, classes, and objects | Supports all OOP concepts |
| Does not support function and operator overloading | Supports function and operator overloading |
| Function-driven language | Object-driven language |
C++ was designed to be a superset of C, meaning that valid C code is also valid C++ code. However, C++ introduced several new features and concepts, such as classes, objects, and OOP, which significantly expanded the language‘s capabilities and made it more suitable for developing complex, modular, and maintainable software.
8. What is the difference between struct and class?
The primary differences between struct and class in C++ are:
| Aspect | struct | class |
|---|---|---|
| Default Access Modifier | Members are public by default. | Members are private by default. |
| Memory Allocation | Can be allocated on the stack or heap. | Can be allocated on the stack or heap. |
| Inheritance | Supports inheritance (with public, protected, or private access). | Supports inheritance (with public, protected, or private access). |
| Use Case | Often used for Plain Old Data (POD) structures, or simple data grouping. | Suitable for complex objects that may include methods, constructors, and destructors. |
The main distinction is the default access modifier: struct members are public by default, while class members are private by default. This difference can influence the way you design and use these user-defined data types in your C++ programs.
9. What is the difference between reference and pointer?
The main differences between references and pointers in C++ are:
| Reference | Pointer |
|---|---|
| The value of a reference cannot be reassigned. | The value of a pointer can be reassigned. |
| It can never hold a null value as it needs an existing value to become an alias of. | It can hold or point at a null value and be termed as a nullptr or null pointer. |
To access the members of a class/struct, it uses a . operator. | To access the members of a class/struct, it uses a -> operator. |
| The memory location of a reference can be accessed easily or it can be used directly. | The memory location of a pointer cannot be accessed easily as we have to use a dereference * operator. |
References are generally simpler and more intuitive to use than pointers, as they provide a more natural way to work with variables. However, pointers offer more flexibility and control, particularly when dealing with dynamic memory allocation and low-level system programming.
10. What is the difference between function overloading and operator overloading?
| Function Overloading | Operator Overloading |
|---|---|
| It is the process of defining a function in multiple ways, such that there are many ways to call it. | It is the process of giving a special meaning to an existing operator or redefining the pre-defined meaning. |
| Parameterized functions are a good example of function overloading, as you can change the argument or parameter of a function to make it useful for different purposes. | Polymorphism is a good example of operator overloading, as an object of one class can be used and called by different classes for different purposes. |
Example: int GFG(int X, int Y); int GFG(char X, char Y); | Example: int GFG() = X() + Y(); int GFG() = X() - Y(); |
Both function overloading and operator overloading are examples of compile-time polymorphism, where the compiler determines the appropriate function or operator to use based on the provided arguments or operands.
11. What is the difference between an array and a list?
| Arrays | Lists |
|---|---|
| Arrays are contiguous memory locations of homogeneous data types stored in a fixed location or size. | Lists are individual elements that are linked or connected to each other with the help of pointers and do not have a fixed size. |
| Arrays are static in nature. | Lists are dynamic in nature. |
| Arrays use less memory than linked lists. | Lists use more memory as they have to store the value and the pointer memory location. |
Arrays are generally more efficient for storing and accessing data, as the elements are stored in contiguous memory locations. Lists, on the other hand, offer more flexibility in terms of dynamic resizing and insertion/deletion operations, but come with the overhead of managing the pointers between elements.
12. What is the difference between a while loop and a do-while loop?
while Loop | do-while Loop |
|---|---|
| Also termed an "entry-controlled" loop. | Also termed an "exit-control" loop. |
| If the condition is not satisfied, the statements inside the loop will not execute. | Even if the condition is not satisfied, the statements inside the loop will execute at least once. |
Example: while(condition) { statements; } | Example: do { statements; } while(condition); |
The main difference between these two loop structures is the order in which the condition is evaluated. In a while loop, the condition is checked before the loop body is executed, while in a do-while loop, the loop body is executed at least once before the condition is checked.
13. Discuss the difference between prefix and postfix?
| Prefix | Postfix |
|---|---|
| The operator is placed before the operand. | The operator is placed after the operand. |
| It executes itself before the statement. | It executes itself after the statement. |
Associativity of prefix ++ is right to left. | Associativity of postfix ++ is left to right. |
The primary distinction between prefix and postfix operators lies in the order of execution. Prefix operators perform the increment/decrement operation before the value is used, while postfix operators perform the operation after the value is used. This difference can lead to subtle differences in the behavior of your code, so it‘s important to understand when to use each form.
14. What is the difference between new and malloc()?
new | malloc() |
|---|---|
new is an operator that performs an operation. | malloc() is a function that returns and accepts values. |
new calls the constructors. | malloc() cannot call a constructor. |
new is faster than malloc() as it is an operator. | malloc() is slower than new as it is a function. |
new returns the exact data type. | malloc() returns void*. |
The primary distinction between new and malloc() is that new is an operator specifically designed for dynamic memory allocation in C++, while malloc() is a more generic memory allocation function inherited from C. new is generally preferred in C++ code, as it can automatically call constructors and return the exact data type, making it more type-safe and convenient to use.
15. What is the difference between virtual functions and pure virtual functions?
| Virtual Functions | Pure Virtual Functions |
|---|---|
| A virtual function is a member function of a base class that can be redefined in a derived class. | A pure virtual function is a member function of a base class that is only declared in the base class and defined in the derived class. |
| A virtual function has its definition in the base class. | There is no definition in a pure virtual function, and it is initialized with a pure specifier (=). |
| The base class can be represented or instanced (i.e., its object can be made). | A base class having a pure virtual function becomes an abstract class that cannot be represented or instanced (i.e., its object cannot be made). |
Virtual functions are a key component of runtime polymorphism in C++, allowing derived classes to override the behavior of base class functions. Pure virtual functions, on the other hand, are used to create abstract base classes that serve as interfaces or contracts for derived classes to implement.
16. What are classes and objects in C++?
A class is a user-defined data type where all the member functions and data members are tailored according to the requirements. To declare a user-defined data type, we use the class keyword.
An object is an instance of a class and an entity with value and state. In simple terms, it is used as a catalyst or to represent a class member. An object may contain different parameters or none.
A class is a blueprint that defines functions which are used by an object. By encaps