Showing 21–30 of 100 questions
in Pointers
How does free() handle a NULL pointer?
A
Causes segmentation fault
B
Does nothing (safe operation)
C
Returns error code
D
Undefined behavior
Correct Answer:
B. Does nothing (safe operation)
EXPLANATION
free(NULL) is safe in C and does nothing. This is by design to prevent errors when freeing pointers.
What is the purpose of the const keyword in: int * const p;?
A
Pointer points to constant data
B
Pointer itself is constant
C
Both pointer and data are constant
D
Data becomes read-only
Correct Answer:
B. Pointer itself is constant
EXPLANATION
const after * means the pointer address cannot change, but the data it points to can be modified.
In the expression: int arr[5]; int *p = arr; What does p + 2 represent?
A
Address of arr[0] + 2 bytes
B
Address of arr[2]
C
Value 2
D
Address of arr[0] + 8 bytes
Correct Answer:
B. Address of arr[2]
EXPLANATION
Pointer arithmetic scales by data type size. p + 2 moves 2 * sizeof(int) bytes forward, pointing to arr[2].
What is the difference between NULL and a wild pointer?
A
NULL points to 0, wild is uninitialized
B
Both are same
C
NULL is a constant, wild can vary
D
NULL is type-safe, wild is not
Correct Answer:
A. NULL points to 0, wild is uninitialized
EXPLANATION
NULL is explicitly set to address 0, while wild pointers contain garbage values from uninitialized memory.
Which operation is NOT allowed on void pointers in C without explicit casting?
A
Assignment
B
Arithmetic operations
C
Dereferencing
D
Passing to functions
Correct Answer:
B. Arithmetic operations
EXPLANATION
Void pointers cannot perform pointer arithmetic (++, --, +n) directly. They must be cast to a specific type first.
Consider the code: int x = 10; int *p = &x; int **q = &p; What is the value of **q?
A
10
B
Address of x
C
Address of p
D
Undefined
EXPLANATION
q points to p, p points to x. **q dereferences twice: first gets p's value (address of x), second gets x's value (10).
What is the size of a pointer in a 64-bit system?
A
2 bytes
B
4 bytes
C
8 bytes
D
16 bytes
Correct Answer:
C. 8 bytes
EXPLANATION
In 64-bit systems, pointers are 8 bytes (64 bits) regardless of the data type they point to.
Which of the following correctly declares a pointer to a pointer?
A
int **ptr;
B
int *&ptr;
C
int &&ptr;
D
int ***ptr;
Correct Answer:
A. int **ptr;
EXPLANATION
Double pointer (int **ptr) is the correct syntax for pointer to pointer. Single & is used in C++ references, not C.
What is the output?
int arr[] = {10, 20, 30};
int *p = arr;
printf("%d", sizeof(p));
A
12
B
8 or 4 depending on system
C
3
D
Compilation error
Correct Answer:
B. 8 or 4 depending on system
EXPLANATION
p is a pointer, so sizeof(p) returns pointer size (8 bytes on 64-bit, 4 on 32-bit), not array size.
What is the difference between arr and &arr if arr is an array?
int arr[5];
A
Both are identical
B
arr is pointer to first element, &arr is pointer to whole array
C
&arr is pointer to first element, arr is pointer to whole array
D
They have different sizes
Correct Answer:
B. arr is pointer to first element, &arr is pointer to whole array
EXPLANATION
arr decays to pointer to first element (int*). &arr is pointer to whole array (int(*)[5]). Pointer arithmetic differs.
