Top 30 Programming Interview Questions and Answers

The interviewer wants to know your knowledge of the core concept of Programming.

Sample Answer:

Computer Programming is the process of designing and writing instructions for a computer to execute. It involves problem-solving, logic-building, and using Programming languages like Java, Python, or C++ to develop software applications. This is one of the most common topics in basic interview Programming questions, especially for entry-level roles.

They want to know how you approach identifying and resolving code issues.

Sample Answer:

Debugging is the act of detecting and fixing bugs or defects in a program. It often involves using tools like IDE debuggers, print statements, or logging to trace and isolate the problem, ensuring the software behaves as expected.

To check your understanding of how values are stored and used in code.

Sample Answer:

A variable is a named storage location that holds data during a program’s execution. Its value can change as the program runs. Variables are essential for performing operations, storing user input, or managing dynamic data. They’re a core concept in all programming languages and are commonly used to test basic understanding of memory and logic flow.

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To test your conceptual view of code execution and software logic.

Sample Answer:

Programming involves writing code that the computer interprets or compiles into machine-readable instructions. These instructions control hardware behaviour, process data, and automate tasks to achieve a desired outcome. This concept is frequently asked in basic Programming interview questions to test a candidate’s foundational understanding of how code executes.

They want to test your understanding of function self-calls.

Sample Answer:

Recursion is a technique where a function calls itself to solve a problem by breaking it down into smaller instances of the same problem. I use it when a task can be defined in terms of similar sub-tasks.

Example:

Output:

This continues until a base condition is met, making it ideal for problems like tree traversals or factorials.
 

To evaluate your understanding of Object-oriented Principles.

Sample Answer:

Object-oriented Principles like encapsulation, inheritance, abstraction, and polymorphism are frequently included in the best Programming Interview Questions to assess your ability to design robust, scalable code.

They want to test your optimisation and problem-solving skills.

Sample Answer:

To solve the Fibonacci sequence efficiently, I use dynamic programming to store previously calculated values and avoid redundant computations. Instead of using simple recursion, I create a list to store Fibonacci numbers up to n. I start with fib[0] = 0 and fib[1] = 1, then use a loop to fill the rest:

Using Dynamic Programming:

Output:

To test your understanding of recursion and tree structures.

Sample Answer:

“To find the depth of a binary tree, I use recursion to explore both left and right subtrees. For each node, I calculate the depth of its left and right children, then return the greater of the two plus one. The base case is when the node is None, in which case I return 0. This approach helps me determine the longest path from the root to any leaf node.”

Example:

To evaluate basic error understanding.

Sample Answer:

“I define division by zero as an invalid mathematical operation that leads to a runtime error in programming. Since dividing any number by zero isn't possible, I make sure to handle it using conditional checks or try-except blocks. This helps me prevent crashes and ensures my program runs smoothly even when unexpected inputs occur.”

They want to check if you understand modular Programming.

Sample Answer:

“I understand a subroutine as a block of code also called a function or procedure that performs a specific task. I use subroutines to break down complex programs into smaller, manageable parts. They help me avoid repeating code, make my logic easier to follow, and promote reusability across different parts of a program.”

To test your knowledge of data structures.

Sample Answer:

Linked lists are ideal when frequent insertions or deletions are needed, especially in the middle of the list. Unlike arrays, they don't require resizing and allow dynamic memory allocation.

To assess your familiarity with fundamental types.

Sample Answer:

Data types define the type of data a variable can hold. Common types include int, float, char, and Boolean. For instance, in Java: int age = 30; declares an integer variable.

To see your grasp of algorithm goals.

Sample Answer:

“I often come across searching and sorting problems that test my problem-solving and optimisation skills. I use searching to locate specific elements, like with binary search, and sorting to organise data, such as with merge sort. I make sure to understand the time complexity of each approach so I can choose the most efficient algorithm for the problem.”

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To test your understanding of immutability.

Sample Answer:

In Java, strings are final and immutable for security, thread safety, and caching. Once created, their value can't be changed, preventing accidental modifications and allowing memory optimisations like string pooling.

To assess your basic logic and loop use.

Sample Answer:

“I reverse a number by using a loop to extract each digit and build the reversed number step by step. I take the last digit using n % 10, add it to the new number after shifting its digits, and then remove the last digit from the original number using n //= 10. This method is simple and commonly appears in basic programming interview questions to test logic and loop control. For example, reversing 12345 gives me 54321.”

Example:

Output:

To test knowledge of concurrency issues.

Sample Answer:

“A deadlock occurs when two Por more threads are waiting Ifor each other’s Qresources indefinitely. It usually happens due to circular dependencies. Avoiding nested locks and using lock timeouts can prevent it.”

To assess your knowledge of code execution flow.

Sample Answer:

“A compiler interprets high-level code into machine code. It performs lexical analysis, syntax checking, optimisation, and finally generates executable code, enabling programs to run directly on hardware.”

To evaluate your understanding of mutable vs immutable strings.

Sample Answer:

In Java, a String is immutable once created, its value cannot be changed. Any modification results in a new object being created, which can lead to memory inefficiency. StringBuilder, on the other hand, is mutable and allows in-place changes, making it more suitable for operations that involve frequent concatenation, especially within loops or iterative processes. This helps improve performance and reduces memory overhead.

To check your familiarity with code validation.

Sample Answer:

A syntax error occurs when code violates the grammatical rules of a programming language such as missing a semicolon, misplacing brackets, or using incorrect keywords. These errors are usually caught during compilation or interpretation and prevent the program from running. They're often straightforward to fix but require careful attention to language-specific syntax.

Example:

Error removed:

To test debugging and logic applications.

Sample Answer:

A logical error occurs when a program runs without crashing but produces incorrect or unintended results. It happens due to flaws in the algorithm or incorrect implementation of logic like using the wrong operator or condition. These errors can be tricky to detect since they don’t generate error messages and require thorough testing or step-by-step tracing to fix.

To evaluate your grasp of algorithm efficiency.

Sample Answer:

Big O notation describes the worst-case time or space complexity of an algorithm as the input size increases. It helps measure performance and scalability. For example, O(n) means linear growth, while O(1) means constant time regardless of input size. Understanding Big O is crucial for writing efficient code and choosing the most suitable algorithm for a given problem.

To test your basics on fixed values.

Sample Answer:

The two types of constants are literal constants and symbolic constants. Literal constants are fixed values written directly in the code, like 42 or 'A'. Symbolic constants use names, such as const PI = 3.14, to represent fixed values. Constants help maintain data integrity and are commonly used in configuration settings, formulas, and values that shouldn't change during execution.

To assess your knowledge of functional Programming.

Sample Answer:

A pure function is one that always returns the same output for the same input and doesn’t cause any side effects, such as modifying external variables. They are important because they make code more predictable, easier to test, and safer to reuse. In functional programming, pure functions help maintain clarity and reduce bugs by isolating logic from external dependencies.

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To test your knowledge of control flow.

Sample Answer:

“I use nested loops when I need to repeat a set of actions within another loop, like iterating through rows and columns in a matrix. They’re useful for tasks such as pattern printing, grid-based problems, or comparing elements in two arrays. I make sure to manage loop variables carefully to avoid unnecessary iterations or logic errors.”

Example:

Output:

To test your problem-solving using maths or iteration.

Sample Answer:

“I find the missing number by first calculating the expected sum of numbers from 1 to 100 using the formula n(n + 1)/2, which gives 5050. Then I subtract the actual sum of the array from this value. The difference tells me which number is missing. It’s a quick and efficient approach that avoids checking each element individually.”

Use the formula sum of n numbers:

missing = n*(n+1)/2 - sum(array)

This is efficient and avoids extra space or iterations”

To assess your error-handling awareness.

Sample Answer:

Many interview questions involve stack (LIFO) and queue (FIFO) operations. LIFO removes the last-added item first, like undo functions, while FIFO removes the first-added, like task queues. Knowing when to use each is important in tasks involving memory handling or process scheduling.

To test understanding of stack and queue behaviour.

Sample Answer:

LIFO (Last-In-First-Out) is used in stacks, where the last element added is the first removed. FIFO (First-In-First-Out) is used in queues, where the first element added is the first removed. LIFO suits tasks like undo operations, while FIFO is ideal for scheduling and buffering.

To test your knowledge of machine-oriented code.

Sample Answer:

“I see low-level programming languages like Assembly as closer to hardware. They let me control memory and CPU directly, which is useful for system-level tasks. But they’re harder to write and understand than high-level languages.”

To evaluate your dynamic Programming knowledge.

Sample Answer:

“Memoisation uses recursion and caches results, while tabulation builds the solution iteratively using a table. Both optimise overlapping subproblems but differ in approach top-down vs bottom-up.”

The interviewer wants to test your understanding of how values are stored and manipulated in variables during program execution.

Sample Answer:

Assignment operators frequently appear in Programming Interview Questions to test your understanding of variable manipulation. They help assign and update values efficiently, like using x += 5 instead of x = x + 5. These operators are often used in loops, calculations, and conditionals to simplify code and improve readability.