Preparing for a technical interview but not confident with C programming Interview Questions? Don’t worry, we’ve got you covered! In this article, we’re going to cover the 20 most important and commonly asked C program interview questions that you might encounter in technical interviews.Â
Our team has carefully selected and crafted these questions after extensive research and analysis of industry trends. We’ve looked into the kinds of questions that top companies are asking, reviewed feedback from candidates who have gone through these interviews, and consulted with industry experts to ensure that these questions will help you to prepare effectively. Whether you’re a beginner or looking to brush up on your skills, these questions are designed to give you a solid foundation and boost your confidence for your upcoming interview.
1) What is the C language?
Ans) C programming language is known as a mid-level and procedural language. This means that it uses a method where big programs are divided into smaller, manageable parts or modules. Each part follows a structured code, which helps in reducing errors and misunderstandings in the program.
2) Why is C called the mother language?
Ans) C is often referred to as the “mother language” because many other programming languages, such as C++, Python, Rust, and JavaScript, have been developed based on it. Additionally, many important tools like compilers and JVMs are written in C. It also introduced many key concepts like arrays, functions, and file handling, which are used in other languages.
3) Why is C called a mid-level programming language?
Ans) C is considered a mid-level language because it bridges the gap between low-level and high-level programming languages. This means it can be used for system programming like developing operating systems and application programming like creating customer billing systems.
4) What are the features of the C language?
Ans) Despite being one of the oldest programming languages, C is still used widely by developers and software engineers for variety of purposes. We have mentioned below some of the key features of C, that make it a standout choice in the market:
- Simple: C is easy to understand because it uses a structured approach by breaking down programs into smaller parts.
- Portable: Programs written in C can run on different machines with little or no changes which makes it a flexible choice.
- Mid-Level: C combines features of both low-level and high-level languages.
- Structured: C programs are organized in a structured way, making them easy to understand.
- Fast Speed: C is very fast due to its efficient use of data types and operators.
- Memory Management: C has built-in functions that help in managing memory and making programs more efficient.
- Extensible: C can easily adopt new features, making it adaptable for future use.
5) What is the use of printf() and scanf() functions?
Ans)Â printf(): This function is used to display various types of data, like integers, characters, floats, and strings, on the screen. Different format specifiers are used with printf() functions, such as:
- %d: To print an integer.
- %s: To print a string.
- %c: To print a character.
- %f: To print a floating-point number.
scanf(): This function is used to take input from the user.
6) What is the difference between a local variable and a global variable in C?
Ans) Local and global are two different types of variables found in C programming languages, Here’s a comparison between local and global variables which will help you to understand it better:
C Program Interview Questions- Local And Global Variables | ||
Basis | Local Variable | Global Variable |
Declaration | Declared inside a function or block. | Declared outside any function or block. |
Scope | Available only within the function where it’s declared. | Available throughout the entire program. |
Access | Accessible only by the function where it’s declared. | Accessible by any part of the program. |
Life | Exists only while the function is running. | Exists as long as the program is running. |
Storage | Stored in the stack, unless specified otherwise. | The compiler decides where to store it. |
7) What is the use of a static variable in C?
Ans) A static variable is a special type of variable that generally keeps its value between function calls. Here’s why static variables are useful:
- They retain their value even after the function in which they are declared finishes executing.
- Static variables are accessible throughout the program which makes them useful for sharing a common value across different parts of the program.
- They are initialized only once in the memory, which helps programmer to save memory and improve efficiency.
8) What is the use of functions in C?
Functions in C are useful because they:
- Help in avoiding the repetition of the same code multiple times in a program.
- Functions can be called from any part of the program, multiple times.
- Functions make it easier to track and manage different parts of a program.
- It promote reusability by breaking down large tasks into smaller, more manageable ones.
9) What is the difference between call by value and call by reference in C?
Ans) Call by value and call by reference are two important parts of the C programming language, Let us understand each of these terms in a better way by seeing the comparison between call by value and call by reference given below:
C Program Interview Questions – Call By Value Vs Call By Reference | ||
Feature | Call by Value | Call by Reference |
Description | A copy of the value is passed to the function; the original value remains unchanged. | The actual memory address is passed, so the original value can be modified. |
Memory Location | The function creates separate memory locations for actual and formal arguments. | The same memory location is used for both actual and formal arguments. |
Safety | Original values are safe and cannot be altered by the function. | Original values can be modified, making them less safe. |
Arguments | Copies of the actual arguments are passed to the function. | Memory addresses of the actual arguments are passed to the function. |
Let us understand both of these terms in a better way by looking at the practical examples of both of them.Â
Example of call by value |
#include <stdio.h>Â Â
void change(int,int);  int main()  {      int a=10,b=20;      change(a,b); //calling a function by passing the values of variables.      printf(“Value of a is: %d”,a);      printf(“\n”);      printf(“Value of b is: %d”,b);      return 0;  }  void change(int x,int y)  {      x=13;      y=17;  }  |
Output-Â
Value of a is: 10 Value of b is: 20 |
Practical Example Of Call By Reference |
#include <stdio.h>Â Â
void change(int*,int*);  int main()  {      int a=10,b=20;      change(&a,&b); // calling a function by passing references of variables.      printf(“Value of a is: %d”,a);      printf(“\n”);      printf(“Value of b is: %d”,b);      return 0;  }  void change(int *x,int *y)  {      *x=13;      *y=17;  }  |
Output-Â
Value of a is: 13 Value of b is: 17 |
10) What is Recursion in C?
Ans) Recursion happens when a function calls itself. The function that does this action is called a recursive function. There are two main phases in recursion:
- Winding Phase: This is when the function keeps calling itself with new arguments until a certain condition is met.
- Unwinding Phase: This starts when the condition is met. The function then returns to the original call, completing the process.
Example Of Recursion |
#include <stdio.h>Â Â
int calculate_fact(int);  int main()  {   int n=5,f;   f=calculate_fact(n); // calling a function   printf(“factorial of a number is %d”,f);    return 0;  }  int calculate_fact(int a)  {    if(a==1)    {        return 1;    }    else    return a*calculate_fact(a-1); //calling a function recursively.     }  |
Output-Â
factorial of a number is 120 |
11) What is an Array in C?
Ans) An array is a collection of items of the same type stored in a sequence. It uses a single name and has a fixed size. The size and type of the array cannot be changed once it is created. There are two types of arrays that are used in C programming language, These two include:
- One-Dimensional Array: This is like a list of items. For example, a list of numbers or names.
- Multidimensional Array: This is like a table with rows and columns. For example, a grid of numbers.
12) What is a Pointer in C?
Ans) A pointer is a variable that holds the address of another variable. Instead of holding a value directly, it holds the location where the value is stored. Pointers are mainly denoted by (*) and They are used for making the code more efficient and faster. Let us understand the pointers better with the help of a practical example given below-Â
Example Of Pointer |
#include <stdio.h>Â Â
int main()Â Â {Â Â Â Â Â int *p; Â Â Â //pointer of type integer. Â Â Â Â int a=5;Â Â Â Â Â p=&a;Â Â Â Â Â printf(“Address value of ‘a’ variable is %u”,p);Â Â Â Â Â Â return 0;Â Â }Â Â |
Output-Â
Address value of ‘a’ variable is 428781252 |
13) What is the Usage of Pointers in C?
Ans)
- Accessing Array Elements: Pointers can help you to move through arrays.
- Dynamic Memory Allocation: Pointers are used to manage memory that is allocated during the program’s run time.
- Call by Reference: Pointers let you pass a reference to a variable into a function.
- Data Structures: Pointers are used to create complex data structures like trees, graphs, and linked lists.
14) What is a NULL Pointer in C?
Ans) A NULL pointer is a pointer that does not point to any valid memory location. It is often assigned a value of `0`. Using NULL pointers basically helps a developer to avoid errors when the pointer is not yet assigned a valid address.
15) What is a Far Pointer in C?
Ans) A far pointer can access all memory segments in a computer system. It is a 32-bit pointer which is generally used in older systems to manage large memory spaces single handedly.
16) What is a Dangling Pointer in C?
Ans) A dangling pointer occurs when a pointer still points to a memory location that has been freed or deallocated. This can cause problems because the pointer is no longer valid. To fix this issue, you should set the pointer to NULL after freeing the memory.
17) What is a Pointer to Pointer in C?
Ans) A pointer to a pointer is a variable that stores the address of another pointer. It creates a chain of pointers. For example, if `p` is a pointer to an integer, then `q` can be a pointer to `p`.
18) What is Static Memory Allocation?
Ans) Static memory allocation means allocating memory at compile time, before the program runs. Once the static memory is being allocated in the program the memory size cannot change afterwards. This type of memory is used for arrays and is faster to access.
19) What is Dynamic Memory Allocation?
Ans) Dynamic memory allocation happens at runtime that allows the program to allocate memory as needed while it runs. This is used for structures like linked lists. The functions used in dynamic memory allocations are written below for your reference:
- malloc(): Allocates memory without initializing it.
- calloc(): Allocates memory and initializes it to zero.
- realloc(): Changes the size of previously allocated memory.
- free(): Releases the allocated memory when it’s no longer needed.
Q20) What is a Structure?
Ans) A structure is a way to group different types of data together into a single unit. You can consider it like a container that holds various kinds of information. Each piece of information in a structure is called a member. The total memory used by a structure is the sum of the memory needed for all its members. You can only access the members of a structure through a structure variable. Different structure variables can use different amounts of memory, even if they use the same structure.
Q21) What is a Union?
Ans) A union is similar to a structure in that it can hold different types of data. However, unlike a structure, a union only uses enough memory for its largest member. This means all members of the union share the same memory space. You can only use one member of the union at a time, as the memory is shared among all members.
Q22) What is the Auto Keyword in C?
Ans) In C programming, the auto keyword is used for local variables inside functions. Local variables are only accessible within the function where they are declared. By default, these variables are called automatic or auto variables. You don’t have to use the auto keyword in the program. If you don’t assign a value to an auto variable, it may contain a garbage value, which is just random data left in that memory space.
Learn C++ With PW Skills
Join our comprehensive DSA with C++ Course and master the basics and fundamentals of C++ programming with guidance from industry experts. Learn and practice simultaneously with our free online PW Lab Compiler and regular doubt sessions. This course offers comprehensive tutorials on Data Structures and Algorithms, as well as hands-on programming classes which will surely help you in learning all the concepts related to CÂ programming Interview Questions.
Enroll now to start your journey into an exceptional programming journey with us at pwskills.com.
Error handling in C can be done using multiple methods like- checking return values from functions, checking for error codes, and using functions from the errno.h library. There is no built-in exception handling like in some other languages. A segmentation fault occurs when a program tries to access a memory location that it's not allowed to. This is usually due to bugs such as dereferencing null or uninitialized pointers. Break is used to exit from a loop or switch statement prematurely, while continue statement is used for skipping the remaining code in the current iteration of a loop and proceeds with the next iteration.C Program Interview Questions FAQs
How do you handle errors in C programs?
What is a segmentation fault?
What are break and continue statements used for?