30 Most Asked Programming Interview Questions You Must Know

by Muhammad Talha
Programming Interview Questions

A Programming Interview is something any developer faces at least once or may face multiple times in their career. No matter which programming job role you are applying for it’s important to know the basic programming concepts that are always expected from you in an interview.

With so many programming languages out there, knowing which one to focus on when trying to find a job can be challenging. So it’s very crucial to know which interview questions are more likely to be asked of you. In this article, we are going to discuss the most asked programming interview questions along with their answers to help you to crack those interviews and get your dream job.

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We’ve grouped these questions into two categories which are,

  1. Conceptual programming Interview Questions
  2. Coding Questions

Let’s begin with the first part which is conceptual questions in programming.

Conceptual Programming Interview Questions

This part covers the coding interview questions along with their answers that test the conceptual knowledge of the candidate.

1. What is Computer Programming?

Computer programming is a process of writing code that instructs the computer what to do and how to do it. This process includes writing algorithms, designing, coding, debugging, and maintaining.

A computer program is a set of instructions written by a programmer using a programming language to perform a specific computing task.

2. What is Debugging?

Debugging is a process of detecting and removing errors (also called bugs) in a computer program, software, or system. It is a multi-step process in which a programmer first finds bugs in the source code of any program and then fixes those bugs.

3. What are the different types of errors that occur during the execution of a program?

There are basically three types of errors that usually a programmer faces during the execution of a program.

  1. Logical Error
  2. Syntax Error
  3. Runtime Errors

4. What is a Logical Error?

A logical error occurs in a program when you apply wrong logic in the program and that results in unexpected and incorrect output. Usually while compiling the source code the compiler didn’t detect the logical error in the program. The programmer has to identify and fix it manually.

5. What is Syntax Error?

A syntax error occurs when you violate the syntax rule of a programming language while writing the code. The compiler can easily detect the syntax error and will not compile the source code until all syntax errors are fixed.

6. What is Runtime Error?

A Runtime error occurs during the execution of a program. It happens when you perform an illegal operation in a program such as dividing a number by zero is an unknown operation. When a runtime error occurs the program stops its execution and terminates immediately.

7. What is Data Structure?

A way of storing and organizing data in a computer so that it can be used efficiently and effectively. There are many data structures but the most popular ones are Arrays, Stack, Queue, and Trees.

8. What is an Algorithm?

An Algorithm is a finite set of instructions to perform a particular task. It is a method or process to solve a problem. A good algorithm is clear (having no ambiguity), has a finite set of instructions, must terminate, and must be time and space efficient.

9. What is a Linked List?

A Linked List is a linear data structure in which elements are explicitly ordered, that is each element contains within itself the address of the next element.

It contains a sequence of nodes, and each set of nodes contains two elements.

  • The item is stored in the list
  • A pointer that points towards the next node in the list.
Linked List

Fig: Linked List

10. What is Stack?

A stack is a linear data structure that has an ordered collection of data. In a stack insertion and deletion of data occur at only one end, which is called the Top of the stack.

All the operations are performed in LIFO (Last In First Out) order in a stack. The most common operations in the stack data structure are push(), pop(), top(), and IsEmpty()

Stack Diagram - Programming Interview Questions

Fig: Stack


11. What do you know about a Queue?

A Queue is a linear data structure that follows the FIFO (First In First Out) method. In a queue, the element that is inserted first will be deleted first. There are two ends in a queue one for the insertion of data and the other for removal.

The insertion operation in a queue is known as Enqueue and deletion is known as Dequeue.

Queue diagram

Fig: Queue

12. Differentiate Between FIFO and LIFO?

FIFO stands for First In First Out. It means when data is entered first must leave first. An example of FIFO is a Queue, where the data that enters the queue first is also deleted first.

Whereas, LIFO stands for Last In First Out. It means the data that is entered Last will leave first. An example of LIFO is the Stack, where the data is on the top of the list that is the data entered last will leave the list first.

13. What are Binary Trees?

A binary tree is a set of elements that is either empty or partitioned into three disjoint subsets. The first subset contains a single element and is known as the root. The other two subsets are also binary trees themselves and called left and right subtrees of the root.

Every subtree or element of a binary tree is called the node of the tree.

Binary Tree Diagram

Fig: Binary Tree

14. What is OOP?

Object Oriented Programming (OOP) is an advanced programming paradigm built around ‘Objects’. The key concepts in OOP include Object, Class, Inheritance, Polymorphism, and Abstraction.

OOP Concepts

Fig: OOP

15. What are Pointer Variables?

A pointer is the memory address of a variable in computer memory. A variable that is used to hold a pointer is known as Pointer Variables. The variable that is going to hold the address of the pointer must be of pointer type. For Example,

The variable p holds pointers to variables of type double.

16. What is Recursion?

A recursive function is a function that calls itself either directly or indirectly through another function. Recursion is the most used method in computer science to solve complex problems by breaking them down into simpler ones.

17. What is the Difference Between a Stack and an Array?

Stack Array
A stack is a linear data structure that follows are fixed pattern which is LIFO (Last In First Order). In means that the elements that arrive last on the list will leave the list first. On the other hand, an Array doesn’t follow any order. In an array, elements are stored and accessed through index numbers. Every element in an array has a fixed index number.

18. What is Modeling Language?

Modeling is a graphical or textual computer language that is used to express information or system in a structure and models through a consistent set of rules. A modeling language is used in computer science, and software engineering for constructing structures and models of new software, systems, and devices.

For Example UML (Unified Modeling Language, Flowchart, EXPRESS, Systems Modeling Language, etc).

19. Difference Between Arithmetic and Relational Operators

Arithmetic  Relational
Arithmetic Operators are those operators that are used to perform arithmetic operations on numbers.

e.g. +, -, *, /, % are the arithmetic operators.

Relational Operators are those operators that are used to compare or relate two values. These operators give us either true or false outcomes. They are also called logical operators.

e.g. <, >, <=, >= &&, ==, || are the relational operators.

20. What is software testing?

Software testing is a process and one of the phases of software development of testing the software whether it meets its requirements or not. A process of evaluating and verifying that the software product does what it is supposed to do.

The software testing team finds bugs and errors through various techniques in the software product.

Programming/Coding Interview Questions

The next phase of programming interview questions focuses on coding. We’ve provided code snippets along with the questions to help you understand it with clarity.

21. How to reverse a string in Java?


  • First, declare/define a string
  • Then find the length of the string (You can do it manually or through a built-in function)
  • Initiate a loop through characters of the string
  • Store the output string in a variable and display the result.


String text = "Java";
String rev = "";
int length = text.length();
for(int i=length; i>0; --i)
    rev = rev + text.charAt(i-1);

22. Find the number of occurrences of a character in a string


  • Declare the string and find its length
  • Initiate a count variable to store the number of occurrences of a character
  • Loop through the string
  • In the loop search for the character you want to count and increment the count


String text = "Programming";
int length = text.length();
String search = 'm';
int count = 0;
for(int i=0; i<length; i++)
   if(text.charAt(i) == search)


23. Implement bubble sort algorithm

In a bubble sort algorithm, the whole array is traversed, and compare every element with its next element. If the current element is greater than its next element then they are swapped.


static void bubbleSort(int[] arr)
    int n = arr.length;
    int temp = 0;
    for(int i=0; i < n; i++)
       for(int j=1; j < (n-i); j++)
           if(arr[j-1] > arr[j])
                temp = arr[j-1];
                arr[j-1] = arr[j];
                arr[j] = temp;

24. Find the largest number in an array


  • First, declare an array
  • Declare a variable to store the largest number and initiate with 0.
  • Loop through the array
  • Compare each element in the array with the next element in each iteration, if the next element is greater than the current element, store it in the largest variable.


int arr[10] = {3,5,1,7,9,2,0,6,8,4};
int largest = 0;
for(i=0; i<10; i++)
   if(largest < arr[i])
      largest = arr[i];

25. Implement a binary search algorithm

  • Binary search is the fastest search algorithm that works on the principle of divide and conquers.
  • Binary search looks for a particular element by comparing the middle element of the list.
  • It is mandatory for a binary array that the array needs to be sorted.


int BinarySearch(int a, int n, int key)
   Left = 0;
   Right = n-1;
   while (left <= right)
       Mid = (left +right)/2;
       if (key == a[mid])
           return mid;
       else if (key < a[mid])
           right = mid - 1;
           left = mid +1;
   return -1;


26. How to find the factorial of a number


  • The factorial of a number is multiplying a number by every number below it. For example factorial of 5 is denoted as 5! = 5*4*3*2*1 = 120
  • Declare a variable and initiate it will 1
  • Initiate a for loop
  • Multiple every number on every iteration


int factorial = 1;
int n = 5;
for(int i = 1; i <= n; ++i)
    factorial *= i;

27. How to remove a character from a string

  • You can use a built-in function ‘replace()’ to remove a character from a given string.
  • It requires two parameters, the first one is the character you want to replace and the second parameter is the character you want to replace with.
  • In this case, we are going to remove a character, so we’ll input “” (empty quotes) as a second parameter.


String str = "Java is easy to learn";
String strNew = str.replace("a", "");

28. How to find whether a number is prime or not


  • A prime number is one that is divisible by itself and 1 only.
  • If a number is divisible on any other number then it is not a prime number
  • The numbers 0 and 1 are not prime


if (n == 0 || n == 1)
   return false;
if (n == 2)
   return true;
for (int i = 2; i <= n / 2; i++)
   if (n % i == 0)
      return false;
      return true; 

29. How to sum all elements of an array


  • Declare an array.
  • Declare a variable and initiate with 0.
  • loop through the array.
  • Now add every element of the array on every iteration and store it in the variable.


int arr[] = { 12, 3, 4, 15,10,8 };
int sum = 0;
for (i = 0; i < arr.length; i++)
    sum += arr[i];

30. Explain inheritance with the help of a program

  • Inheritance is a method of creating a hierarchy of objects such that one object acquires all the properties and behavior of its parent object.
  • It represents the Is-A relationship, which is the parent-child relationship.


class A 
   void msg()
class B 
   void msg()
class C extends A, B 
   public static void main(String args[])
       C obj = new C();


That completes our list of programming interview questions. Every passionate programmer should know about these questions as they are the most asked programming interview questions. If find some other questions that you think should be on this list, then comment below and we’ll add those questions to the list. All the best!

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