Top 45 C Programming Viva Questions

If you are preparing for the C programming viva questions, then you have to understand fundamentals. C is a powerful general-purpose programming language that provides the foundation for many modern languages like C++, Java, and Python. It is widely used for system programming, embedded systems, operating systems, and application development due to its speed and efficiency.

Founder of the C Language

The C language was developed by Dennis Ritchie at Bell Labs in the early 1970s. He designed it as an improvement over the B language to help in building the UNIX operating system.

When Was the C Language Developed?

C was created in 1972. It was initially developed to rewrite the UNIX operating system, making it more portable and flexible across different machines.

Why is C Called a Mother Language?

C is frequently called the "mother of all programming languages" for the following reasons:

• Most modern languages borrow their core concepts like loops, functions, and operators.
• It serves as a base for understanding low-level memory operations and hardware interactions.
• Operating systems, drivers, and compilers are often written in C, showcasing its foundational nature.

Key Features of the C Language

Understanding the features is very essential to gain a good knowledge to answer the C programming viva questions. 

• Simplicity: Easy to learn and use, with a clean and structured syntax.
• Speed: Executes programs quickly due to close-to-hardware operations.
• Portability: Code written in C can run on different machines with minimal changes.
• Rich Library: Offers a variety of built-in functions to simplify programming.
• Modularity: Supports functions and reusable code blocks.
• Low-Level Access: Provides the ability to work directly with memory using pointers.

Important topics in the C language include data types, control structures (if-else, loops), functions, arrays, pointers, memory management, and file handling. Understanding structures, preprocessor directives, and dynamic memory allocation is also crucial. Developing effective, reliable applications requires knowledge of these subjects, which are the foundation of C programming viva questions.

Below are a few of the most asked basic viva questions for C programming, which help you understand the fundamentals.

1. What is the C language?
Early in the 1970s, Dennis Ritchie developed the general-purpose computer language C. Because of its effectiveness, portability, and strong connection to hardware, it is frequently utilized in embedded systems, operating systems, and system programming.

2. What are the key features of C?

• Low-level memory access
• Fast performance
• Rich library support
• Structured programming
• Portability
• Simple syntax

3. How is a C variable definition different from a declaration?

• Declaration tells the compiler about a variable’s type and name, but memory is not allocated.
• Definition declares and also allocates memory for the variable.

4. What does the printf() function in C language do?
printf() is used to display output on the screen. It allows formatted output using format specifiers like %d, %f, %s, etc.

5. What is the purpose of the C function scanf()?
scanf() is used to take input from the user during program execution. It uses the conventional keyboard input to read structured data.

6. What makes float in C different from int in C?
int is used to store whole numbers (e.g., 5, -3) while float stores numbers with decimal points (e.g., 3.14, -2.75).

7. What is the role of a pointer in accessing memory in C?
In C programming, a pointer plays a key role in memory access by holding the location of another variable. With this memory address, the pointer allows you to retrieve or change the value stored there. This is especially useful in scenarios like managing arrays, handling dynamic memory, or passing data to functions more efficiently.

8. What exactly is the main() function in C used for?
Every C program begins with the main() function. A C program starts running after this function.

9. What is a constant in C?
A fixed value that cannot be modified while a program is running is called a constant. It is declared using the const keyword or #define.

10. What are keywords in C?
Keywords are reserved words with predefined meanings in C (e.g., int, return, if, while). They cannot be used as variable names.

11. What is a data type in C?
A data type defines the type of data a variable can hold, such as int for integers, char for characters, float for decimals, etc.

12. What are the different types of loops in C?
C supports:

• for loop
• while loop
• do-while loop

13. What is the purpose of the return statement in C?
To leave a function and also return a value to the caller function, use return.

14. What is the difference between = and == in C?
= is the assignment operator, used to assign values.
== is the equality operator, used to compare two values.

15. What is the syntax of the C for loop?

for(initialization; condition; update) {
   // loop body
}

These C viva questions will test your understanding of control structures, functions, arrays, and pointers, helping you prepare for real-time programming scenarios.

1. How does call by reference differ from call by value in C?

• Call by value: A copy of the actual value is passed to the function. Changes made inside the function don’t affect the original value.
• Call by reference: The address of the variable is passed, so any changes inside the function reflect in the original variable.

2. What is recursion in C?
Recursion in programming refers to a technique where a function repeatedly calls itself, breaking down a complex problem into simpler sub-problems, until it reaches a condition that stops further calls (known as the base case).

3. What are storage classes in C?
Storage classes in C determine the scope, duration, and accessibility of variables within a program. Common storage classes in C include:

• auto
• register
• static
• extern

4. How do malloc() and calloc() differ in terms of memory allocation in C?

• malloc(size) allocates uninitialized memory.
• calloc(n, size) in C is used to allocate memory for n items, and it automatically sets all the values to zero.

5. What is a dangling pointer in C?
A dangling pointer refers to a situation where a pointer still points to a memory location that has already been released or deallocated. Accessing such a pointer can result in unpredictable or erroneous program behavior.

6. What is a structure in C?
A user-defined data type called a structure combines linked variables, possibly of multiple data types, under a single name. It helps to organize complex data.

struct Student {
    int id;
    char name[50];
};

7. Why is typedef used in C programming?
typedef is used in C to define a new identifier or alias for an existing data type, making the code more readable and easier to manage.

typedef unsigned int uint;

8. What differentiates union in C from structure?

• Each and every member of a structure has a unique memory location.
• The memory location is the same for all union members. A value can only ever be stored by one member.

9. What is pointer arithmetic in C?
Adding, subtracting, increasing, and decreasing pointers to move between memory addresses of arrays or variables is made possible via pointer arithmetic.

10. What is a null pointer?
A null pointer is a pointer that points to nothing or zero. It is used to indicate that the pointer is not assigned any valid memory address.

int *ptr = NULL;

11. Why is the sizeof operator in C used?
A variable's or data type's memory usage is indicated by the size of operation.

int x;
printf("%d", sizeof(x));  // Output might be 4

12. What makes "continue" different from "break"?

• break: Exits the loop or switch immediately.
• Continue: The continue statement skips the current iteration and jumps to the next loop cycle.

13. What are macros in C?
Code fragments are substituted by macros, which are preprocessor directives written with #define, prior to compilation.

#define PI 3.14

14. What is the function of the static keyword in C?
By utilizing the static keyword, a variable's value is preserved in between function calls. It also limits variable or function scope to the file.

15. Define command-line argument in C
When a program starts, command line arguments are inputs sent from the terminal to the main() method.

int main(int argc, char *argv[])

Explore these important C Programming Viva Questions to strengthen your understanding of advanced concepts.

1. What is dynamic memory allocation in C?
Dynamic memory allocation in C allows the program to allocate memory at runtime using functions like malloc(), calloc(), realloc(), and free(). It provides more flexibility than static memory allocation.

2. What are the differences between C programming's pre-increment and post-increment operators?

Pre-increment (++k) involves increasing the variable k first, and then using the increased value in the expression. Whereas, post-increment (k++) uses the initial value of k in the expression first, followed by the increment.

3. What are the advantages and disadvantages of using goto in C?

Advantages:

• Helps in skipping straight to a particular section of the code.
• Useful to break out of deeply nested loops.
• It can simplify error handling in some cases.

Disadvantages:

• Makes the code hard to read and understand.
• Difficult to maintain and debug.
• Can lead to messy code, known as "spaghetti code."
• Not recommended in modern programming.

4. What is the difference between strcpy() and strncpy() in C?

• strcpy() copies a null-terminated string, assuming the destination has enough space, without any bounds checking.
• strncpy() copies a specified number of characters and ensures that the destination buffer is not overflowed, adding a null terminator if there is room.

5. Describe the concept of bitwise operators in C
Bitwise operators work with numbers that are represented in binary. Common bitwise operators include:

• & (AND)
• | (OR)
• ^ (XOR)
• ~ (NOT)
• << (Left shift)
• >> (Right shift)

6. What is an inline function in C?
An inline function is one where the compiler attempts to insert the code of the function directly into the places where it is called, improving performance by reducing function call overhead.

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

7. What is the difference between struct and enum in C?

• A struct is a data type that allows grouping of variables of different types under a single name.
• An enum is a user-defined data type consisting of named integer constants, useful for creating a set of values.

8. In C, what are function pointers used for?
A program may store function addresses and make dynamic calls to them through function pointers. This provides flexibility in function selection at runtime, commonly used in callback mechanisms.

void (*ptr)(int);
ptr = &function_name;

9. What is the volatile keyword used for in C?
Even if a variable looks unused, the volatile keyword instructs the compiler not to optimize it. This is particularly useful for variables that can change unexpectedly, like hardware registers or shared memory in multi-threaded programs.

10. Explain the concept of a memory leak in C.
A memory leak occurs when a program allocates memory dynamically (using malloc(), calloc(), etc.) but fails to release it (using free()). Over time, this causes the program to consume more memory, eventually leading to system resource exhaustion.

11. What is the difference between fopen() and freopen()?

• fopen() is used to open a file in a specific mode for reading, writing, etc.
• freopen() is used to reassign an existing file pointer to a new file, allowing redirection of standard input/output streams.

12. What is the significance of the exit() function in C?
The exit() function terminates a program immediately, returning a status code to the operating system. It can be used to exit the program from anywhere, including inside a function.

13. How does a stack overflow occur in C?
A stack overflow happens when the program uses more stack space than is allocated, typically due to excessive recursion or creating too large of local variables. This can cause the program to crash or exhibit undefined behavior.

14. What is a segmentation fault in C?
A segmentation fault occurs when a program tries to access memory that it isn’t allowed to, such as accessing an invalid pointer or a memory location outside the bounds of an array.

15. Explain the concept of multithreading in C.
Multithreading allows a program to perform multiple tasks simultaneously by creating independent threads. Each thread runs in its own execution context, allowing for parallel processing, and is often managed using libraries like pthread.

C programming is an essential skill in computer science. Understanding its basics, like syntax, and advanced topics, such as pointers and file handling, is essential for any programmer. Instead of memorizing answers, focus on truly understanding the concepts. This approach will help you perform well in your C programming viva questions and build a strong foundation for a career in software development.