C Programming Interview Questions for Freshers: The 40 Asked in Vivas and Placement Drives

Freshers memorise definitions, then freeze when an interviewer says, "Dry-run this" or "What does this print?" C sits close to memory, so a strong answer explains what exists, where it lives, and when it changes.

Here are 40 questions grouped by the ideas interviewers probe, followed by the answering method you can use at a whiteboard.

How C interviews are scored, not just recalled

Interviewers use pointers, memory, and undefined behaviour to test runtime reasoning. They may accept a definition, then change one line and ask for the effect.

Identify each object's type and lifetime, draw the cells, apply the statement, then state the output. If C does not define an outcome, say undefined behaviour instead of guessing.

Pointers and memory: the core 10

1. What does a pointer hold? An address of an object or function of a compatible type, or a null pointer value that points to no object.

2. What is a pointer to pointer? A pointer whose target is another pointer, such as int **pp; *pp is an int * and **pp is an int.

3. What does pointer arithmetic do? Adding one to int *p advances by one int, provided the result stays within the same array object or one past it.

4. What is array-to-pointer decay? In most expressions, an array name converts to a pointer to its first element; important exceptions include operands of sizeof and unary &.

5. How do arr and &arr differ? They commonly have the same numeric address, but arr decays to a pointer to the first element while &arr points to the entire array and steps by the whole array size.

6. Dangling pointer vs wild pointer? A dangling pointer refers to an object whose lifetime has ended; a wild pointer is uninitialised and holds an indeterminate value.

7. What is a null pointer? A pointer value guaranteed not to compare equal to the address of any object or function; dereferencing it is undefined behaviour.

8. What is void *? A generic object-pointer type that can hold an object address; convert it to an appropriate typed pointer before dereferencing.

9. What is a function pointer? A pointer that stores a function address and can call a function with the matching signature, often used for callbacks.

10. const int *p vs int * const p? The first prevents changing the pointed value through p; the second prevents making p point somewhere else.

Pointers in C for GATE adds memory diagrams.

Worked example: pass-by-pointer mutation

Use this exact program:

void inc(int *p) {
    (*p)++;
}
int main() {
    int a = 5;
    inc(&a);
    printf("%d\n", a);
}

Trace it in memory:

1. a lives in main's stack frame, say at address 0x7ffe1004, holding 5.

2. inc(&a) passes that address; inside inc, p holds 0x7ffe1004.

3. (*p)++ reads the cell reached through p and writes 6 to 0x7ffe1004.

4. Back in main, a is now 6; the output is 6.

If inc took int p by value, a would stay 5 because only a copy would change. Here, the value copied into p is a's address.

Storage, memory layout and lifetime: the core 10

1. Stack vs heap? Automatic local objects usually have block lifetime and are commonly stack-backed; dynamically allocated objects remain until free and come from managed dynamic storage.

2. What does malloc do? It allocates an uninitialised byte block and returns void *, or a null pointer on failure.

3. How do calloc and realloc differ? calloc allocates an array and zero-initialises its bytes; realloc changes an existing allocation and may move it.

4. Why call free? It ends the lifetime of allocated storage; using that pointer to access the freed object afterwards is invalid.

5. What is a memory leak? Allocated memory becomes unreachable without being freed, so the program can no longer release or reuse it deliberately.

6. What is a static local's lifetime? It exists for the entire program and retains its value between calls, although its name remains block-scoped.

7. static vs extern at file scope? static gives internal linkage; extern declares a name whose definition can have external linkage elsewhere.

8. What causes a segmentation fault? Common causes include invalid dereferences, writing read-only storage, out-of-bounds access, and stack exhaustion; C does not guarantee that particular signal.

9. sizeof array vs pointer? In the array's defining scope, sizeof arr is the whole array size; after decay or in a function parameter, sizeof p is only the pointer size.

10. Can you modify a string literal or read an uninitialised automatic variable? No safe result is defined: modifying a literal is undefined behaviour, and reading an indeterminate automatic value can also be undefined behaviour.

Language semantics that trip people: the core 10

1. i++ vs ++i? Both increment i; postfix yields the old value while prefix yields the new value.

2. What does i = i++ do? It has undefined behaviour in C because modifications of i are unsequenced; never offer a numeric answer.

3. How does integer division work? With integer operands, the fractional part is discarded towards zero, so 7 / 2 is 3.

4. What happens in character arithmetic? A char is promoted to an integer type before arithmetic, so 'A' + 1 can be printed as 'B' with %c on ordinary C implementations.

5. What is implicit type promotion? Narrow integer types commonly promote to int or unsigned int, and mixed arithmetic then follows the usual conversions.

6. #define vs const? A macro is token substitution with no C type; a const object has a type, scope, and storage semantics.

7. What is the macro argument trap? Write #define SQR(x) ((x) * (x)); missing parentheses breaks expressions, and passing i++ still causes multiple evaluation.

8. Struct vs union size? A struct provides storage for every member plus padding; a union provides shared storage large and aligned enough for its largest-demanding member.

9. Name two useful bit tricks. XOR can swap two distinct integer objects without a temporary, and positive n is a power of two when (n & (n - 1)) == 0.

10. Switch fallthrough, break, and continue? A case falls through without break; break exits the switch or loop, while continue starts the next loop iteration.

Output and dry-run rapid fire: the remaining 10

How to answer under pressure: the short version

Reason about memory aloud, distinguish values from addresses, and name undefined behaviour. Technical interview prep: OS, DBMS, CN and OOP questions freshers face places C inside the wider plan.

Next, work the concept and MCQ sets in the C Programming course. KnowledgeGate has about 900 published C Programming questions for follow-up practice. For the rest of the drive, combine that work with the Mera Placement Hoga Anushasan bundle or browse the Placement Preparation catalogue.