500+ C Programming Interview Questions with Answer 2026

Detailed Exam Domain CoverageThis comprehensive practice exam framework maps directly to the technical evaluation metrics used by tier-one technology firms, defense contractors, and embedded engineering departments. The questions are categorized into 8 strict domains to isolate and elevate your technical proficiencies:Core Concepts (20%)Topics Covered: Single and multi-dimensional arrays, string manipulation mechanics, pointer fundamentals, string literal pooling, storage classes (auto, extern, static, register), and variable scope/linkage mechanics.Data Structures (18%)Topics Covered: Singly, doubly, and circular linked lists; array-based and pointer-based stacks and queues; binary trees, binary search trees (BST), graph representations (adjacency matrices and lists), and common traversal algorithms.Memory Management (15%)Topics Covered: Dynamic memory allocation (malloc, calloc, realloc), memory deallocation (free), stack vs. heap memory execution, memory leaks, dangling pointers, wild pointers, and memory fragmentation behaviors.Functions and Recursion (12%)Topics Covered: Pass-by-value vs. pass-by-reference emulation using pointers, execution stack frames, recursive depth conditions, tail recursion optimization, and function pointer arrays for dispatch tables.Problem-Solving Skills (10%)Topics Covered: Algorithmic optimization, bitwise operations, dry-running tracking, finding and fixing logical bugs, time and space complexity evaluation, and edge-case code hardening.Advanced Topics (8%)Topics Covered: Structure and union mechanics, alignment rules, anonymous structures, enum evaluation rules, preprocessor macro hazards vs. inline functions, and command-line argument parsing.File Handling and Input/Output (7%)Topics Covered: Stream I/O functions (fopen, fclose, fread, fwrite), file position pointers (fseek, ftell), buffered vs. unbuffered streams, standard I/O redirection, and robust error checking using errno.Scenario-Based Questions (10%)Topics Covered: Hardware-software boundaries, interrupt service routine (ISR) constraints, volatile memory qualification, concurrency race conditions, and optimization for performance-critical systems.Course DescriptionNavigating a technical C programming interview requires much more than just a surface-level understanding of syntax. Because C interfaces directly with hardware and memory architectures, companies hiring for engineering systems look for deep, intuitive reasoning. They will test your ability to predict side effects, prevent memory leaks, manage pointer arithmetic safely, and optimize data layout.I designed this targeted question bank containing 550 high-fidelity practice questions to help you uncover and patch any hidden knowledge gaps in your coding fundamentals. Instead of basic dictionary definitions, these questions challenge your structural problem-solving abilities and diagnostic intuition. Every scenario simulates actual evaluation questions asked during interviews for positions like Embedded Systems Developers, Systems Programmers, and Core Platform Software Engineers.Each question features a comprehensive structural breakdown. I walk you through the precise execution path of code snippets, explaining the exact mechanics of why the correct option is secure and efficient, and why the other alternatives fail due to syntax violations, compiler warnings, or undefined behaviors. Mastering these concepts will give you the underlying technical clarity needed to articulate clean, confident, and accurate answers on your first attempt.Sample Practice Questions PreviewQuestion 1: Core Concepts Pointer Arithmetic PrecedenceWhat is the exact console output of the following valid C program execution block?C#include stdio.h int main() { int arr[] = {10, 20, 30}; int *p = arr; printf("%d ", *p++); printf("%d ", ++*p); printf("%d", *++p); return 0;}A) 10 20 30Why Incorrect: This answer assumes that the operators execute sequentially without shifting the pointer or mutating underlying values in place. It neglects that p++ increments the pointer reference and ++*p modifies data elements directly.B) 10 21 30Why Correct: Let's trace the execution steps. Initially, p points to arr[0] (10). In the first statement, *p++ evaluates to 10 because the postfix increment operator (++) has higher precedence but evaluates after the current value is passed to the expression. The pointer p then moves to arr[1] (20). In the second statement, ++*p applies a prefix increment to the value currently pointed to by p (arr[1]), turning 20 into 21 and printing it. In the final statement, *++p first increments the pointer itself via prefix notation, moving p to arr[2] (30), and then dereferences it to print 30.C) 11 21 31Why Incorrect: This occurs if you mistake the postfix operator *p++ as an immediate increment of the value inside the array element before the first print occurs. Postfix expressions yield the initial value before updating the operand.D) 10 20 20Why Incorrect: This response implies that the pointer p was never incremented to point to the final array index, or that the prefix operations modified temporary copies instead of the real array contents.E) 11 20 30Why Incorrect: This choice wrongly applies a prefix evaluation step onto the initial postfix expression while missing the subsequent destructive modify step on the middle element.F) Compilation Error due to undefined sequence pointsWhy Incorrect: The statements are separated by explicit semicolon tokens representing clear sequence points. There are no competing modifications to the same variable within a single expression, making this fully standard-compliant C code.Question 2: Memory Management Pointer Variable ScopeConsider the following C program segment intended to allocate dynamic memory block space. What behavior occurs when this code runs?C#include stdio.h #include stdlib.h void allocate_memory(int *ptr) { ptr = (int *)malloc(sizeof(int)); *ptr = 100;}int main() { int *p = NULL; allocate_memory(p); if (p == NULL) { printf("NULL"); } else { printf("%d", *p); } return 0;}A) 100Why Incorrect: This assumes that passing the pointer variable p allows the function to modify the address held inside main. In C, pointers are passed by value; modifying the local copy inside the function parameter does not alter the original reference.B) NULLWhy Correct: When you call allocate_memory(p);, a copy of the pointer address (which is NULL) is assigned to the local parameter variable ptr. Inside the function, ptr is updated with a valid address returned by malloc, and that heap space is populated with 100. However, this change only updates the local variable ptr. Once the function scope closes, ptr is destroyed, creating a memory leak on the heap. The pointer p inside main remains completely unchanged as NULL, causing the conditional statement to trigger and display "NULL".C) 0Why Incorrect: This output would imply that p was modified to point to an initialized calloc-style zeroed block, whereas p was never reassigned from its original NULL state.D) Segmentation Fault during executionWhy Incorrect: A segmentation fault would happen if the code attempted to blindly dereference p while it was NULL (e.g., calling *p directly). Because the code explicitly checks if (p == NULL) before accessing the memory location, it executes safely.E) Compilation Error due to invalid pointer assignmentWhy Incorrect: The code follows legal C language syntax constraints. Type casting from malloc matches the target types perfectly, and pointer comparisons are valid, meaning it compiles cleanly without errors.F) Undefined Behavior leading to random garbage valuesWhy Incorrect: The code contains a memory leak, but its logical execution path inside main is deterministic and entirely safe due to the conditional validation guard checking the state of p.Question 3: Advanced Topics Struct Padding RulesAssume a standard 64-bit target compiler environment where a char occupies 1 byte, a short occupies 2 bytes, and an int occupies 4 bytes. What is the output of sizeof(struct Sample) given the structural type definition below?Cstruct Sample { char a; short b; char c; int d;};A) 8Why Incorrect: This represents the unpadded absolute sum of bytes ($1 + 2 + 1 + 4 = 8$). Standard C compilers do not pack elements this tightly by default because doing so violates hardware alignment boundaries.B) 10Why Incorrect: This choice represents incomplete padding calculation tracking where basic 2-byte alignment might be respected but the stricter 4-byte boundaries required for integer types are missed.C) 12Why Correct: Compilers structure data layout based on alignment constraints to optimize bus transactions. The variable char a sits at offset 0. The variable short b requires a 2-byte aligned address boundary; since offset 1 is unaligned, 1 byte of padding is placed after a, putting b at offset 2. Next, char c is placed at offset 4. The variable int d requires a 4-byte aligned boundary. The next open slot is offset 5, so the compiler adds 3 bytes of internal padding (at offsets 5, 6, and 7) to line up d perfectly at offset 8. The structure size reaches 12 bytes, which matches the internal alignment requirement of the largest element (int), leaving the final structural footprint at 12 bytes.D) 16Why Incorrect: This value is generated if the compiler forces every single individual data element to greedily round up to the maximum 4-byte width slot, which wastes more padding space than standard alignment rules require.E) 24Why Incorrect: This calculation assumes that the structure is processing allocations under strict 8-byte word-boundary rules for every member, which is atypical unless 64-bit pointers or double data types are present.F) Compilation Error due to packed structure alignmentWhy Incorrect: Declaring standard primitive variables sequentially inside a structure context is perfectly legal C syntax. The compiler handles the necessary alignment adjustments automatically without throwing faults.Welcome to the Interview Questions Tests to help you prepare for your C Programming Interview Questions.You can retake the exams as many times as you wantThis is a huge original question bankYou get support from instructors if you have questionsEach question has a detailed explanationMobile-compatible with the Udemy appI hope that by now you're convinced! And there are a lot more questions inside the course.