Home › Subjects › C Programming › Dynamic Memory

C Programming
Dynamic Memory

C language from basics to advanced placement prep

100 Q 10 Topics Take Test

Difficulty: All Easy Medium Hard 31–40 of 100

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.31 Easy Dynamic Memory

Which header file must be included to use malloc() and free() functions?

A #include

B #include

C #include

D #include

Correct Answer: A. #include

EXPLANATION

<stdlib.h> is the standard header file containing declarations for malloc(), calloc(), realloc(), and free() functions.

Take Test

Q.32 Easy Dynamic Memory

Which function in C is used to allocate memory dynamically at runtime?

A malloc()

B alloc()

C allocate()

D memalloc()

Correct Answer: A. malloc()

EXPLANATION

malloc() is the standard C library function for dynamic memory allocation. It takes the number of bytes to allocate as an argument and returns a pointer to the allocated memory.

Take Test

Q.33 Hard Dynamic Memory

For implementing a dynamic stack in competitive programming, which memory management approach is best?

A Pre-allocate fixed size array on stack

B Single malloc for max capacity, track top with index

C malloc/free for each push/pop operation

D Use global static array

Correct Answer: B. Single malloc for max capacity, track top with index

EXPLANATION

Single allocation with index tracking minimizes malloc/free overhead, suitable for competitive programming time constraints.

Take Test

Q.34 Hard Dynamic Memory

Consider this: char *p = malloc(10); strcpy(p, "Hello World"); What occurs?

A String is copied successfully

B Buffer overflow - writes beyond allocated 10 bytes

C Null terminator is lost

D Compilation error

Correct Answer: B. Buffer overflow - writes beyond allocated 10 bytes

EXPLANATION

"Hello World" is 11 bytes (including null terminator). Writing to 10-byte buffer causes buffer overflow, corrupting adjacent memory.

Take Test

Q.35 Hard Dynamic Memory

What is a potential issue when allocating very large contiguous blocks (>10^8 bytes) dynamically?

A malloc() always succeeds for any size

B Fragmentation and allocation failure, should check return value

C Integer overflow in size calculation

D Free space is automatically allocated

Correct Answer: B. Fragmentation and allocation failure, should check return value

EXPLANATION

Large allocations may fail due to heap fragmentation or insufficient contiguous memory. Always check malloc() return for NULL.

Take Test

Q.36 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.37 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.38 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.39 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

Q.40 Medium Dynamic Memory

In a competitive programming scenario, you need to store strings dynamically. What is safe practice?

A char *str = malloc(100); without checking for NULL

B char *str = malloc(strlen(input)+1); with NULL check and strncpy

C char str[100] always on stack

D No allocation needed, use global arrays

Correct Answer: B. char *str = malloc(strlen(input)+1); with NULL check and strncpy

EXPLANATION

Safe practice includes allocating exact size (input length + 1 for null terminator), checking for NULL, and using bounded string functions.

Take Test

1 2 3 4 5 6…10

All Subjects & Topics

Medical & Engg

Govt Exams

Teacher Exams

Subjects

Quick Links

C Programming
Dynamic Memory

All Subjects & Topics

Medical & Engg

Govt Exams

Teacher Exams

Subjects

Quick Links

C Programming Dynamic Memory

C Programming
Dynamic Memory