Home › Subjects › C Programming

C Programming

C language from basics to advanced placement prep

499 Q 10 Topics Take Test

Difficulty: All Easy Medium Hard 61–70 of 499

Topics in C Programming

All Basics & Syntax 100 Data Types & Variables 100 Control Flow 100 Functions 100 Arrays & Strings 100 Pointers 100 Structures & Unions 100 File Handling 100 Dynamic Memory 100 Preprocessor 100

Q.61 Medium Dynamic Memory

For storing variable-length strings dynamically in a competitive program, what's the safest approach?

A Allocate strlen(s)+1 bytes to include null terminator

B Allocate strlen(s) bytes

C Use fixed-size char array of 1000

D Allocate 2*strlen(s) for safety

Correct Answer: A. Allocate strlen(s)+1 bytes to include null terminator

EXPLANATION

Strings in C are null-terminated, so allocating strlen(s)+1 bytes ensures space for the null terminator. This is the standard safe approach.

Take Test

Q.62 Medium Dynamic Memory

Which scenario represents a use-after-free error?

A int *p = malloc(10); free(p); p[0] = 5;

B int *p = malloc(10); free(p); free(p);

C int *p = malloc(10); int *q = p; free(p);

D free(NULL);

Correct Answer: A. int *p = malloc(10); free(p); p[0] = 5;

EXPLANATION

In option A, after free(p), the memory is deallocated. Accessing it with p[0] = 5 is a use-after-free error, leading to undefined behavior.

Take Test

Q.63 Medium Dynamic Memory

In the 2024-2025 competitive exam pattern, a dynamic array needs to grow from 100 to 200 elements. Using realloc(), what should be the concern?

A Old pointers to the array may become invalid after realloc()

B realloc() always allocates new memory

C Data is lost during realloc()

D realloc() is slower than malloc() + memcpy()

Correct Answer: A. Old pointers to the array may become invalid after realloc()

EXPLANATION

If realloc() needs to relocate the memory block to a different address, all old pointers to the array become invalid. Only the returned pointer should be used.

Take Test

Q.64 Medium Dynamic Memory

Which of the following is a memory leak?

A int *p = malloc(100); p = malloc(50);

B int *p = malloc(100); free(p);

C int *p = malloc(100); p = NULL;

D int *p = malloc(100); int *q = p;

Correct Answer: A. int *p = malloc(100); p = malloc(50);

EXPLANATION

In option A, the first malloc(100) block becomes inaccessible after p is reassigned, but it's not freed, causing a memory leak. The original 100 bytes are lost.

Take Test

Q.65 Medium Dynamic Memory

What is the critical issue with this code snippet?
int *ptr = (int*)malloc(10);
ptr[11] = 5;

A Buffer overflow - accessing beyond allocated memory

B Memory leak - malloc not paired with free

C Type casting error

D NULL pointer dereference

Correct Answer: A. Buffer overflow - accessing beyond allocated memory

EXPLANATION

malloc(10) allocates 10 bytes, but accessing ptr[11] goes beyond the allocated boundary, causing a buffer overflow which leads to undefined behavior and potential segmentation fault.

Take Test

Q.66 Medium Dynamic Memory

In a competitive programming problem, you need to allocate a 2D array of size 5x5 dynamically. Which approach is most efficient?

A Allocate single block of 25 integers and use 2D indexing

B Allocate 5 pointers, then allocate 5 integers for each pointer

C Use stack allocation with fixed size

D Use global arrays instead of dynamic allocation

Correct Answer: A. Allocate single block of 25 integers and use 2D indexing

EXPLANATION

Allocating a single contiguous block is more cache-efficient and requires only one malloc() call, making it better for competitive programming where memory access speed matters.

Take Test

Q.67 Medium Dynamic Memory

In 2024-2025 competitive exams, for storing variable number of test cases (up to 10^5), which approach is optimal?

A Fixed array of size 10^5

B Dynamic allocation with exact size needed

C Multiple calls to realloc() as data arrives

D Use stack allocation for speed

Correct Answer: B. Dynamic allocation with exact size needed

EXPLANATION

Reading input size first, then allocating exact size is optimal for memory efficiency and avoids repeated realloc() overhead.

Take Test

Q.68 Medium Dynamic Memory

What is the critical issue with this code? int *p = (int*)malloc(sizeof(int)); free(p); p = NULL;

A Cast to (int*) is unnecessary

B Setting p=NULL after free is good practice but not done immediately

C No issue, this is safe practice

D malloc size is too small

Correct Answer: C. No issue, this is safe practice

EXPLANATION

This shows safe practice: allocation, use, freeing, and immediately setting pointer to NULL to avoid use-after-free.

Take Test

Q.69 Medium Dynamic Memory

For a graph with V vertices and E edges stored dynamically, what is typical space complexity?

A O(1)

B O(V + E) for adjacency list, O(V²) for adjacency matrix

C O(E²)

D O(V*E)

Correct Answer: B. O(V + E) for adjacency list, O(V²) for adjacency matrix

EXPLANATION

Adjacency list uses dynamic allocation proportional to V+E, while matrix uses fixed V² space regardless of actual edges.

Take Test

Q.70 Medium Dynamic Memory

A program uses realloc() to expand an array from 100 to 200 elements. The old address is p. After realloc():?

A p still points to old memory location

B p is automatically updated to new location

C Must assign returned value: p = realloc(p, ...)

D The array content is lost

Correct Answer: C. Must assign returned value: p = realloc(p, ...)

EXPLANATION

realloc() returns a new pointer (old location may move). Must use: p = realloc(p, newsize) and check for NULL.

Take Test

1…5 6 7 8 9…50

All Subjects & Topics

Medical & Engg

Govt Exams

Teacher Exams

Subjects

Quick Links

C Programming