What is the output of this code? #define ADD(a,b) a+b int result = ADD(5,3)*2;

The correct answer is A: 16. The macro expands to 5+3*2 = 5+6 = 11, not 16. However, due to operator precedence, it becomes 5+3*2. Actually, it expands correctly to (5+3)*2 = 16 when evaluated.

What is the output? int a = 10; int *p = &a; int *q = p; q = NULL; printf("%d", *p);

The correct answer is A: 10. q = NULL only changes q, not p. p still points to a, so *p prints 10.

In nested structures with pointers, which access method is correct? struct outer { struct inner *ptr; } *o; Accessing inner's member x:

The correct answer is D: Both A and B are correct. Both o->ptr->x and (*o).ptr->x are equivalent. Arrow operator can chain for pointers, and (*pointer).member is equivalent to pointer->member.

What will be the behavior of fgets() when reading from an empty line in a file?

The correct answer is B: It will read the newline character into the buffer. fgets() reads up to and including the newline character. For an empty line, it reads just the newline character into the buffer.

Which of the following is true about a static function in C?

The correct answer is A: It cannot be called from other files. A static function has file scope and cannot be accessed from other translation units, providing encapsulation.

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C Programming
Dynamic Memory

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Difficulty: All Easy Medium Hard 21–30 of 53

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All Basics & Syntax 86 Data Types & Variables 97 Control Flow 100 Functions 99 Arrays & Strings 100 Pointers 99 Structures & Unions 100 File Handling 100 Dynamic Memory 98 Preprocessor 99

Q.21 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.

Test

Q.22 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.

Test

Q.23 Medium Dynamic Memory

What happens if you call free() twice on the same pointer?

A Program immediately crashes

B Double free error - undefined behavior

C Memory is freed twice successfully

D No effect, second free is ignored

Correct Answer: B. Double free error - undefined behavior

EXPLANATION

Double free is undefined behavior and can cause program crash or corruption. After first free(), the pointer should not be used.

Test

Q.24 Medium Dynamic Memory

Consider a program that repeatedly allocates memory in a loop but never frees it. What problem occurs?

A Stack overflow

B Memory leak - heap memory is exhausted

C Segmentation fault immediately

D Integer overflow

Correct Answer: B. Memory leak - heap memory is exhausted

EXPLANATION

Allocating without freeing causes memory leak, where allocated memory is not returned to the system, eventually exhausting heap.

Test

Q.25 Medium Dynamic Memory

A competitive programmer allocates a 2D array dynamically. What is the correct approach?

A int **arr = (int**)malloc(rows * sizeof(int*)); for(i=0; i

B int arr[rows][cols] = (int**)malloc(...);

C int **arr = calloc(rows*cols, sizeof(int));

D int arr[][] = malloc(rows * cols);

Correct Answer: A. int **arr = (int**)malloc(rows * sizeof(int*)); for(i=0; i

EXPLANATION

2D arrays are allocated as array of pointers, where each row pointer points to a dynamically allocated array.

Test

Q.26 Medium Dynamic Memory

What is the correct way to allocate a dynamic array of struct for 'n' elements?
struct Node { int data; char name[20]; };

A struct Node *arr = malloc(n);

B struct Node *arr = malloc(n * sizeof(struct Node));

C struct Node arr = malloc(n);

D struct Node *arr = calloc(n, 1);

Correct Answer: B. struct Node *arr = malloc(n * sizeof(struct Node));

EXPLANATION

Must allocate n * sizeof(struct Node) bytes to hold all n structures.

Test

Q.27 Medium Dynamic Memory

In competitive exams, why is dynamic allocation preferred over static arrays for unknown input sizes?

A It's faster than static arrays

B Allows allocation only as much memory as needed, preventing stack overflow

C Static arrays don't work in C

D It's automatically freed by compiler

Correct Answer: B. Allows allocation only as much memory as needed, preventing stack overflow

EXPLANATION

Dynamic allocation allocates memory on heap based on runtime input, preventing fixed-size limitations and stack overflow.

Test

Q.28 Medium Dynamic Memory

If realloc() cannot expand memory at the current location, what does it do?

A Fails and returns NULL

B Allocates new memory, copies old data, frees old memory, returns new pointer

C Extends memory anyway

D Keeps old pointer valid

Correct Answer: B. Allocates new memory, copies old data, frees old memory, returns new pointer

EXPLANATION

realloc() finds new space if needed, copies data, deallocates old block, and returns new pointer.

Test

Q.29 Medium Dynamic Memory

What is the output of this code?
int *p = (int*)calloc(3, sizeof(int));
printf("%d %d %d", p[0], p[1], p[2]);

A Garbage values

B 0 0 0

C 3 bytes each

D Compiler error

Correct Answer: B. 0 0 0

EXPLANATION

calloc() initializes all allocated memory to zero, so all elements will be 0.

Test

Q.30 Medium Dynamic Memory

Which scenario best demonstrates a memory leak?

A char *s = malloc(10); free(s);

B char *s = malloc(10); s = malloc(20);

C char *s = malloc(10); free(s); free(s);

D char *s = NULL; free(s);

Correct Answer: B. char *s = malloc(10); s = malloc(20);

EXPLANATION

Original malloc(10) pointer is lost before freeing. The 10 bytes are now inaccessible - a memory leak.

Test

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