Top 30 C++ Interview Questions and Answers

C++ can be described as a better version of the C programming language. The cross-platform language with a general purpose can help programmers gain increased control over system memory and resources. Knowing how to answer the most common C++ interview questions is the best way to show employers that you are the right fit for the job. Dive deeper to learn about the most common CPP interview questions and how to answer them.

C++ Interview Questions for Freshers

C++ interview can be very difficult to get into, so it's important to know what you're getting into. We bring to you the top C++ Interview Questions asked with sample answers that would help demonstrate your knowledge of the industry and the job role. 

Some of the most basic C++ interview questions are as follows:

1. What is object-oriented programming (OOP), and how does C++ support it?

   Object-oriented programming is data-focused, with an object as the primary programming unit. C++ can enable OOP with the help of different classes. 

2. Explain the difference between C and C++.

   It is one of the C++ interview questions that you must be able to answer to impress the interviewer. A few key differences between the two programming languages are as follows:

   C	C++
   Procedure-oriented	Object-oriented
   Does not facilitate data hiding	Enables data hiding
   Subset of C++	Superset of C
   Lacks function and operator overloading	Allows function and operator overloading
   Functions are not definable within structures.	Functions are definable within structures.

3. What are the key features of C++?

   It is one of the C++ interview questions and answers that interviewers expect all candidates to know. A few key features of the C++ programming language are as follows:

   • Machine independent
   • Object-oriented programming
   • High-level language
   • Case-sensitive
   • Dynamic memory allocation
   • Compiler based

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4. Explain the concept of inheritance in C++.

   It is one of the easiest CPP interview questions for beginners. Inheritance refers to extending and reusing existing classes without altering them. As a result, hierarchical relationships get established between them. Inheritance is somewhat similar to embedding objects within classes. 

5. What is polymorphism in C++? Provide an example.

   Polymorphism in C++ makes a particular object or function act differently in multiple scenarios. In simple terms, it revolves around conveying the same message in different ways. For instance, the "+" operator is useful for performing different functions in different scenarios.

   Let’s move to the next c++ interview question.

6. How is the function overloading different from the function overriding in C++?

   Overloading refers to multiple functions having the same name with different parameters. Overriding in C++ involves redefining a function with the same name and signature as the inheriting class.

7. What are access specifiers in C++? Explain their significance.

   Access specifiers in the C++ programming language are leveraged to define the way of accessing different attributes and methods of a class. You will find three types of access specifiers in C++:

   • Public: Members can be accessed externally from the class.
   • Private: Members can be viewed or accessed externally from the class.
   • Protected: Members are inaccessible outside the class. But the protected access specifiers can be accessed within inherited classes.

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

   It is one of the most frequently asked C++ interview questions to freshers. A class is a user-defined data structure with a keyword class containing functions and data similar to its members. Objects are data structures that can be defined as class instances. 

   Let’s move to the next c++ interview questions.

9. What is the difference between struct and class?

   It is one of the trickiest CPP interview questions. A structure in C++ is quite similar to a class except for a handful of differences. A few differences between struct and class are as follows:

   Struct	Class
   Struct members are public by default.	Class members are private by default.
   While deriving a struct from a struct or class, the default access specifiers will be public.	While serving a class, the default access specifiers remain private.

   Read: Advantages and Disadvantages of Arrays in C, C++, and Java

Let’s move to the c++ interview questions for intermediate.

C++ Interview Questions for Intermediate

A few CPP interview questions for the intermediate level are as follows:

1. 1. How is a shallow copy and a deep copy in C++ different?

      A C++ shallow copy will store a copy of the original object while finally copying only the reference address. A deep copy will store a copy of the original object along with repetitive copies. 

   2. Explain the concept of function templates in C++.

      Function templates in C++ can be described as special functions operating with generic types. The functionality of these templates can be adapted to more than one class without having to repeat the whole code. In C++, this process is achieved with the help of template parameters. 

   3. What are the differences between class templates and function templates?

      You should be using the class template for creating a class parameterized by any particular type. A function template is for creating a function operating on different types. 

      Function templates are capable of performing type deduction. They can be employed to develop factory functions:

      //Deduces the types of T1 and T2, so
      //for example, a pair<int, double> can be created
      //by `make_pair(10, 1.2)`
      template
      pair<T1, T2> make_pair(T1&& t1, T2&& t2) {
          return {std::forward(t1), std::forward(t2)};
      }
      

      Class templates are utilized to code programs executed at the time of compilation. Class templates are executed using types like values and template instantiations with patterns aligning as pure functions. One example of this is the class template set removing const from a type:

      //Removes all `const` from a type, for example:
      //`remove_const_recursive::type`
      //is the type `int*volatile`.
      template struct remove_const_recursive { typedef T type; };
      template struct remove_const_recursive {
          typedef typename remove_const_recursive::type volatile type;
      };
      template struct remove_const_recursive {
          typedef typename remove_const_recursive::type volatile type;
      };
      template struct remove_const_recursive {
          typedef typename remove_const_recursive::type type;
      };
      template struct remove_const_recursive<T&> {
          typedef typename remove_const_recursive::type& type;
      };
      template struct remove_const_recursive<T*> {
          typedef typename remove_const_recursive::type* type;
      };
      

      Let’s move to the next c++ interview questions.

   4. Explain the concept of operator overloading in C++ with an example.

      It is one of the most important C interview questions. Operator overloading can be defined as a polymorphism for compilation time. This technique can help assign a special meaning to any existing operator without modifying its real meaning. 

      In the C++ programming language, operators are used for user-defined classes. Therefore, C++ can assign a special meaning to operators for a specific data type. This ability can be titled operator overloading. 

      For instance, you can overload an operator "+" in a String class. It will ensure that you can concatenate more than one string with the help of the + operator. Some other classes where arithmetic operators might be overloaded include complex numbers, big integers, and fractional numbers. 

      Example:
      // C++ Program to Demonstrate the 
      // working/Logic behind Operator
      // Overloading
      class A {
          statements;
      };
        
      int main()
      {
          A a1, a2, a3;
        
          a3 = a1 + a2;
        
          return 0;
      }
      
      
      In this example, the type class A has 3 variables called a1, a2, and a3. This example involves adding two objects, a1 and a2, which belong to the user-defined type. But it's not allowed because the addition operator + is only used for operating on in-built data types. 
      
      But in this example, class A is user-defined, which will make the compiler generate an error. That's where the concept of operator overloading can be applied. 
      
      If you want to make the + operators add two class objects, you will have to redefine it in a way that it can add two class objects. The concept of operator overloading can help with it. The primary purpose of operator overloading is to use operators alongside class objects or variables. 
      

What are the differences between virtual functions and pure virtual functions in C++?

It is one of the C++ interview questions and answers to demonstrate your awareness regarding different functions. The difference between virtual functions and pure virtual functions are as follows:

virtual()
{
// code
}

virtual()
= 0;

1. What is the "auto" keyword in C++ 11? How is it used?

   C++11 makes the auto keyword a new type specifier. It serves as a placeholder to deduce a type from the initial variable expression. As auto type deduction gets enabled, you won't be required to mention a type during variable declaration. Instead, the compiler will deduce the type of an auto variable from its initializer expression. One example of the auto-type deduction is as follows:

   auto x = 1; //x : int
   float* p;
   auto x = p; //x : float*
   auto* y = p; //y : float*
   double f();
   auto x = f(); //x : double
   const auto& y = f(); //y : const double&
   class R; 
   R* h();
   auto* x = h(); //x : R*
   auto y = h(); //y : R*
   int& g();
   auto x = g(); //x : int
   const auto& y = g(); //y : const int&
   auto* z = g(); //error, g() does not return a pointer type
   

2. Explain the concept of function objects (functors) in C++.

   The function objects in C++ are useful for implementing operators (). Function objects are primarily used in the C++ standard library as container sorting criteria in algorithms. 

   Let’s move to the next c++ interview questions.

3. Explain the concept of multiple inheritances in C++.

   The feature of multiple inheritance in C++ enables a class to inherit from multiple classes. The inherited class constructors are called in the same order as their inheritance. 

4. What is the purpose of the "mutable" keyword in C++?

   The keyword mutable is utilized for modifying a specific data member of a const object. After declaring a function as const, the pointer passed to the function turns into const. When a mutable gets added to a variable, it can enable a const pointer to modify members. 

   Understand: Fibonacci series in C

Let’s move to the c++ interview questions for experienced.

C++ Interview Questions for Experienced

A few C++ interview questions and answers for experienced professionals are as follows:

1. What is the Rule of Three (Rule of Five) in C++? Why is it important?

   These rules are used for creating exception-safe codes with formalized rules about resource management. These rules are useful for determining the usage of default class members to systematically achieve goals.

2. What are the differences between the "new" and "malloc" functions in C++? Which one should you prefer and why?

   Malloc() and new are useful for allocating dynamic memory in a heap. The malloc() operator is a valuable C library function, also applicable in C++. You should prefer new when you are required to call the constructor class.

   Let’s move to the next c++ interview question.

3. What is the method of compiling a program without utilizing the main function?

   You will be able to compile a program without the main() function by using macros. The code for it is as follows:

   // C++ program to demonstrate the
   // a program without main()
   #include 
   
   #define fun main
   int fun(void)
   {
   printf("Herovired");
   return 0;
   }
   

4. Explain the concept of move semantics and rvalue references in C++.

   The move semantics and rvalue references in C++ can help avoid irrelevant copies while working with temporary objects. They don't copy the temporary, which disappears anyway. Therefore, the resources necessary for temporary objects can be used for other objects. 

5. What is an example of a parameterized constructor?

   The parameterized constructor can accept arguments or parameters. It can be called explicitly by passing values in the arguments. These arguments enable object initialization during its creation. The parameterized constructor will feature the same name as that of the class and can be used to overload constructors. An example of the parameterized constructor is as follows:

   // CPP program to demonstrate
   // parameterized constructors
   #include 
   
   using namespace std;
   class GFG {
   private:
   int x, y;
   public:
   // Parameterized Constructor
   GFG(int x1, int y1)
   {
   x = x1;
   y = y1;
   }
   int getX() { return x; }
   int getY() { return y; }
   };
   int main()
   {
   // Constructor called
   GFG G(10, 15);
   // Access values assigned by constructor
   cout << "G.x = " << G.getX() << ", G.y = " << G.getY();
   return 0;
   }
   Output:
   G.x = 10, G.y = 15
   

   Let’s move to the next c++ interview question.

6. What is a virtual destructor?

   A virtual destructor in C++ is applied in the base class to prevent the derived class object from getting destroyed. An example of this is as follows:

   #include   
   using namespace std;  
   class Base  
   {  
       public:  
       Base()  
       {  
           cout<<"Base constructor is called"<<"n";  
       }  
       ~Base()  
       {  
           cout<<"Base class object is destroyed"<<"n";  
       }  
   };  
   class Derived:public Base  
   {  
       public:  
       Derived()  
       {  
           cout<<"Derived class constructor is called"<<"n";  
       }  
       ~Derived()  
       {  
           cout<<"Derived class object is destroyed"<<"n";  
       }  
   };  
   int main()   
   {  
     Base* b= new Derived;  
     delete b;  
     return 0;  
       
   }  
   Output:
   Base constructor is called
   Derived class constructor is called
   Base class object is destroyed
   

   Let’s move to the next c++ interview question.

7. Write a code to use vectors in C++.

   #include  
   #include  
   using namespace std;  
   int main()  
   {  
   vector  vec_1;  
   vec_push_back("sample code");  
   vec_push_back("change example");  
   for(vector ::iterator i=vec_begin();i!=vec_end();++i)  
   cout<<*i;  
   return 0;   
   } 
   

8. What is the code to sort vectors in C++?

   #include <bits/stdc++.h> 
   using namespace std; 
   int main() 
   { 
       vector vec{ 1,9,4,3,2,8,5,7}; 
       sort(vec.begin(), vec.end()); 
       for (auto x : v) 
           cout << x << "" ""; 
       return 0; 
   }
   

   Find out: What is Arrays in C, C++

Conclusion

In this guide we have discussed some of the most important and common C++ interview questions with answers. Once you are prepared with these C++ interview questions, you have a greater chance of getting the selected in the interview and crack the offer. When you are able to answer these questions, the interviewer will develop a certain level of trust in your skills. Therefore, keep expanding your C++ knowledge to impress employers and quality for high-paying jobs. 

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