25 Most Common C Interview Questions & Answers [For Freshers]

C is a powerful general-purpose programming language that supports procedural, imperative, and structured paradigms. It is used for developing operating systems, databases, and application software for a wide range of computer architectures (PLCs, embedded systems, etc.). C is an excellent beginner-friendly language with an easy learning curve. 

Anyone aspiring to build a career in Software Development must master the basics of C. Once you have learned the nitty-gritty of the C programming language, you will be ready to crack the C interview!

In this blog, we’ll walk you through some of the most commonly asked C interview questions. Typically, a job interview commences by testing your basic knowledge of the subject (in this case, C programming language) and gradually moves on to exploring your practical skills in the domain. The following article will also highlight some of the most asked interview questions on C++. 

So, without further ado, let’s check out the 25 most frequently asked C interview questions!

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C Interview Questions & Answers

1. What are the core features of C?

The first one to make it to the list of the top interview questions on C is this one asked most frequently. To answer the same, you can frame it in this manner. The C programming language is:

• Mid-level – C combines the best features of low-level and high-level languages to create a mid-level, refined programming language.
• Structured – C is a structured language, meaning that C programs are segmented into multiple parts.
• Portable – Once you write a program in C, you can run it on any machine with minimal or no alterations. 
• Fast – C uses an assortment of data types and operators, making it highly speedy and efficient. 
• Extensible – C is highly extensible since it can seamlessly adapt to new features.
• Memory management – C has an inbuilt memory function that saves memory and improves the C program’s efficiency.

2. Which datatypes does C support?

C has four categories of data types:

• Basic data type
• Derived data type
• Enumerated data type
• Void data type

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3. Explain “Dangling Pointer Variable” in C language.

In C programming, a pointer indicates the memory location or address of an existing variable. However, if that variable is deleted and the pointer directs to the same memory location, it is called the Dangling Pointer Variable.

4. What is a “Pointer on Pointer?”

A “Pointer on Pointer” refers to a pointer variable that holds the address of another pointer variable. In essence, the pointer de-refers twice to indicate the data contained in the designated pointer variable.

5. Define an “Array.”

An array is a data structure containing multiple elements of the same datatype in an organized manner. Arrays are usually of three types: one-dimensional, two-dimensional, and three-dimensional. 

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6. What is a Static variable? Why are static variables used in C?

A static variable is one that is declared by the “Static” keyword. A static variable retains its value between multiple function calls. 

The static variable is used as a common value shared by all the methods and is initialized only once in the memory heap to reduce the memory usage. While the static variable is initially initialized to zero, if you update the value of a variable, the updated value will be assigned. 

7. Define the “scope” of a variable.

The scope of a variable refers to the part of the code (function) wherein the variable is declared. In C programming language, all identifiers are either statically or lexically scoped. 

8. What is Dynamic Memory Allocation?

Dynamic Memory Allocation is the procedure of allotting memory to the C program and its variables during runtime. While malloc(), calloc(), and realloc() allocates memory, the free() function frees up the used memory space. 

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9. Explain the difference between calloc() and malloc() functions. 

In C, both calloc() and malloc() are memory allocating functions that allocate memory from the heap area (dynamic memory). The primary difference between the two memory allocating functions is that calloc() loads all the assigned memory locations with the value 0 while malloc() does not.

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10. Explain “Static Memory Allocation.”

Unlike Dynamic Memory Allocation that allocates memory in runtime, Static Memory Allocation allocates the memory during compilation. Static Memory Allocation does not let you increase the memory allocation while the C program is being executed. You can implement the static memory using stacks/heap and allocate the memory using the “Static” keyword. Generally, Static Memory Allocation requires more memory space to store variables than Dynamic Memory Allocation.

11. Name some C Tokens?

A Token is an identifier. It is usually the smallest unit in a C program. Constants, Strings, Keywords, Operators, Identifiers, and Special Characters are a few C Tokens used in writing C programs. 

12. Will a C code compile or execute without a main() function?

In the absence of a main() function, the C program will compile instead of executing because the main() function is mandatory to run any C program.

13. Define a “Nested Structure.”

A Nested Structure is created when an element or data member of a function contains a data member of another structure. 

14. Distinguish between Actual and Formal parameters.

Actual parameters are sent from the primary function to the subdivided function, and the parameters declared as the Subdivided function are known as Formal parameters.

15. What is a Preprocessor Directive?

A Preprocessor Directive is an inbuilt predefined function that functions as a directive to the compiler to perform specific tasks before the compilation process commences. Thus, a Preprocessor Directive is always executed before a C program is executed. 

16. Define “Command Line Arguments.”

The arguments passed on to the main() function during the execution of a C program are known as Command Line Arguments. The first argument denotes the count of arguments and is automatically updated by the operating system. The second argument (an array of character pointers) always contains strings as the parameters. 

17. How can you assign parameters to functions?

There are two ways to assign parameters to functions:

• Call by value – This method is chosen only when you do not want to alter the actual parameters with formal parameters, so you only send a copy of the values as parameters to functions. 
• Call by reference – In this approach, you send the actual parameters’ address to modify them using formal parameters.

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18. What is a “Union” in C?

In C, a Union is a user-defined data type that can store multiple data types in a single unit. It only contains the memory of the largest member instead of the total memory of all members. Since a Union allocates a shared space for all members of a union, you can only access one variable at a time in a Union. 

19. Explain “Recursion.”

Recursion is when a function calls itself, and the function that calls itself is known as a recursive function. A recursive function occurs in two stages:

• Winding phase – When a recursive function calls itself and meets the desired condition, the winding phase ends. 
• Unwinding phase – Once the winding phase is reached, the unwinding phase initiates by returning the control to the original call.

20. How to declare a function in C?

You can declare a function in C like so:

return_type function_name(formal parameter list)
{
       Function_Body;
}

21. What does the sprintf() function do?

The sprintf() function is used to print strings. It fetches the total number of characters in a string. This function transfers the data to the buffer, and hence, it does not print the output on the screen. The syntax of the sprintf() function is:

int sprintf ( char * str, const char * format, … );  

22. Distinguish between getch() and getche() functions?

In a C program, the getch() function reads a single character from the keyword. Since it does use any buffer, it will not display the data you enter on the screen. On the contrary, while the getche() function also reads a single character from the keyword, it shows the data on the screen. 

23. What is “Rvalue” and “Ivalue”?

Rvalue is the expression that lies on the right side of the assignment operator. It is assigned to the Ivalue that lies on the assignment operator. The lvalue must only refer to a variable and not a constant.

24. Name the different storage class specifiers in C.

In C, there are four storage specifiers:

• Auto 
• Static
• Register 
• Extern 

25. Is there any difference between declaring a header file with” “and < >?

If you declare a header file using ” “, the compiler searches for the header file in the current working directory, and if it does not find the file there, it probes other locations for finding the header file. However, if you declare the header file using < >, the compiler searches for the file following the built-in path.

Interview Questions On C++

While C and C++ might sound similar, they are not. C++ is generally considered to be an advanced version of C. Till now, we have looked at some of the frequently asked interview questions on C. The below-mentioned list will highlight some of the top-asked interview questions on C++. So let’s get started.

Q: Can you name some differences between C and C++?

Ans: Both C and C++ are programming languages, with one major difference. While C is a procedure-oriented language, C++ is an object-oriented language. Furthermore, C does not make use of namespace features, which are widely used by C++ in order to avoid name collisions. Last but not least, functions cannot be defined inside the structure of the procedure-oriented language, whereas the same can be defined in the case of C++. 

Q: Can you name the different data types present in C++?

Ans: Yet another one to make it to the list of the top asked C programming interview questions is this one. To put it simply, four different data types are present in C++. They are

• Primitive Data Type
• User-defined data type
• Derived datatype, and 
• Enumeration. 

Q: Can you state the difference between a structure and a class?

Ans: In C++, class and structure are almost similar to each other, except for a few differences related to security. For example, the members of the structure are public, whereas, in class, the members are private by default. Simultaneously, while deriving a class, the default access specifiers are private, whereas, in structure, the default access specifiers are public.

Q: What is meant by a polymorphism in C++?

Ans: To put it simply, polymorphism basically refers to the ability to have different behaviours in different situations. This is especially prevalent in multiple classes that are related to one another by inheritance. Typically, two types of polymorphism exist in C++. They are Runtime polymorphism and Compile time polymorphism. 

Q: What are the three access specifiers of C++?

Ans: In C++, there are typically three different access specifiers, namely, public, private, and protected. Public access specifier, as the name suggests itself, means all data members and member functions can be easily accessed outside the class. In private access specifiers, the complete opposite happens, meaning data members and member functions cannot be accessed outside the class. Protected access specifier, on the other hand, means that the data members and functions are only accessible inside the class, as well as to the derived classes.

With this, we come to an end to the various C language interview questions. These are some of the most frequently asked C programming interview questions that every aspirant should look out for. Additionally, there are also multiple videos and tutorials of C, and C++ available online, on several platforms, such as YouTube, that you can check out to answer C language interview questions like these with finesse. 

Check out: 15 Interview Tips to Stand Out in Your Job Interview

Conclusion

So, there you go: 25 C interview questions and answers to help you prepare for your next job interview. Although these questions only scratch the surface of C programming, hopefully, they’ll give you an idea of what you can look forward to in C interviews!

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