Dynamic memory allocation MCQs

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1. : What is dynamic memory allocation?
(A) Allocating memory at compile time
(B) Allocating memory at runtime
(C) Allocating memory for global variables
(D) Allocating fixed-size memory

2. : Which function is used to allocate memory dynamically in C?
(A) malloc()
(B) alloc()
(C) reserve()
(D) new()

3. : What is the return type of the malloc() function?
(A) int
(B) void*
(C) char*
(D) float*

4. : What happens if malloc() fails to allocate memory?
(A) It returns NULL
(B) It returns 0
(C) It crashes the program
(D) It returns a garbage value

5. : Which function is used to free dynamically allocated memory in C?
(A) release()
(B) dealloc()
(C) free()
(D) dispose()

6. : What is the purpose of the calloc() function?
(A) To allocate memory for a single variable
(B) To allocate memory and initialize it to zero
(C) To free memory
(D) To reallocate memory

7. : What is the difference between malloc() and calloc()?
(A) malloc() initializes memory to zero
(B) calloc() allocates memory for a single variable
(C) malloc() does not initialize memory, while calloc() does
(D) There is no difference

8. : What does the realloc() function do?
(A) Allocates new memory
(B) Frees memory
(C) Changes the size of previously allocated memory
(D) Initializes memory to zero

9. : What is a potential risk of dynamic memory allocation?
(A) Memory leaks
(B) Stack overflow
(C) Underflow
(D) Array out of bounds

10. : Which of the following is true about dynamic memory?
(A) It is automatically deallocated
(B) It must be manually deallocated
(C) It is always faster than static memory
(D) It cannot be resized

11. : What is the purpose of the sizeof operator in dynamic memory allocation?
(A) To determine the size of the pointer
(B) To allocate memory for a pointer
(C) To determine the size of data types
(D) To free allocated memory

12. : What is the outcome of using free() on a pointer that is already freed?
(A) Undefined behavior
(B) Memory leak
(C) No effect
(D) Program termination

13. : In which scenario would you use dynamic memory allocation?
(A) When the size of the data is known at compile time
(B) When creating static arrays
(C) When the size of the data is determined at runtime
(D) When using global variables

14. : What is a common use case for dynamic memory allocation?
(A) Storing constants
(B) Managing arrays of unknown size
(C) Allocating memory for stack variables
(D) Defining global variables

15. : Which function is used to allocate memory for a specific number of elements in C?
(A) alloc()
(B) malloc()
(C) calloc()
(D) reserve()

16. : What happens if you forget to free dynamically allocated memory?
(A) The memory is automatically freed
(B) It causes a segmentation fault
(C) It leads to memory leaks
(D) It has no effect

17. : What is the difference between stack and heap memory?
(A) Stack memory is slower than heap memory
(B) Heap memory is automatically managed, stack is not
(C) Stack memory is used for dynamic allocation, heap is not
(D) Stack memory is used for function calls, heap is for dynamic allocation

18. : What is a memory leak?
(A) When memory is allocated but not freed
(B) When memory is freed too early
(C) When memory is allocated more than needed
(D) When memory is accessed after being freed

19. : What type of memory allocation does the new operator perform in C++?
(A) Static memory allocation
(B) Automatic memory allocation
(C) Dynamic memory allocation
(D) Stack memory allocation

20. : What is the purpose of the delete operator in C++?
(A) To allocate memory
(B) To free memory
(C) To resize memory
(D) To initialize memory

21. : What is the syntax to allocate an array of integers dynamically in C?
(A) int* arr = new int[10];
(B) int* arr = malloc(10 * sizeof(int));
(C) int arr[10];
(D) int arr = allocate(10 * sizeof(int));

22. : What will happen if you try to access memory that has already been freed?
(A) The program will run normally
(B) It will cause a memory leak
(C) It may cause undefined behavior
(D) It will print an error message

23. : How do you check if malloc() succeeded?
(A) Check if the pointer is not NULL
(B) Check if the pointer is -1
(C) Check if the pointer is 0
(D) Check if the pointer is greater than 0

24. : Which of the following can lead to fragmentation in dynamic memory allocation?
(A) Using realloc()
(B) Frequent allocation and deallocation
(C) Using malloc()
(D) Using calloc()

25. : What is the typical overhead for dynamic memory allocation?
(A) 0 bytes
(B) A few bytes per allocation
(C) A few kilobytes per allocation
(D) No overhead

26. : Which function can be used to determine the number of bytes allocated to a pointer in C?
(A) sizeof()
(B) sizeof(pointer)
(C) malloc()
(D) free()

27. : What does realloc() return if it fails to allocate the requested memory?
(A) NULL
(B) -1
(C) 0
(D) The original pointer

28. : In C++, what happens to dynamically allocated memory when the program exits?
(A) It is automatically freed
(B) It remains allocated
(C) It leads to memory leaks
(D) It is set to NULL

29. : Which of the following scenarios requires dynamic memory allocation?
(A) Fixed-size arrays
(B) Variable-length data structures
(C) Global variables
(D) Constant data

30. : What is the memory allocation technique called when the size of memory is not known beforehand?
(A) Static allocation
(B) Dynamic allocation
(C) Automatic allocation
(D) Global allocation

31. : Which of the following statements about memory allocation is false?
(A) Dynamic memory allocation allows for more flexible memory usage
(B) Static memory allocation is faster than dynamic allocation
(C) Dynamic memory allocation is more efficient for large data structures
(D) Dynamic memory allocation guarantees no fragmentation

32. : Which of the following functions is used for memory allocation in C++?
(A) alloc()
(B) new()
(C) malloc()
(D) allocate()

33. : What is the purpose of the new[] operator in C++?
(A) To allocate memory for a single object
(B) To allocate memory for an array of objects
(C) To free memory
(D) To check memory usage

34. : What will happen if you forget to use delete on a dynamically allocated object in C++?
(A) The program will run correctly
(B) The memory will be freed automatically
(C) It will lead to a memory leak
(D) The program will crash

35. : What is the main advantage of using dynamic memory allocation?
(A) It is faster than static allocation
(B) It provides flexibility in memory usage
(C) It uses less memory
(D) It is easier to implement

36. : In C, how do you allocate memory for a structure dynamically?
(A) struct* ptr = malloc(sizeof(struct));
(B) struct* ptr = new struct;
(C) struct* ptr = calloc(1, sizeof(struct));
(D) struct* ptr = allocate(sizeof(struct));

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By: Prof. Dr. Fazal Rehman | Last updated: May 14, 2025

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