Pointers
What is the output of this code?
A
G T
B
G \0
C
G E
D
Compilation error
p points to str[0] which is 'G'. p+3 points to str[3] which is 'E'. Wait - str="GATE" has indices 0:G, 1:A, 2:T, 3:E. So *(p+3) is 'E'. Correction: answer should be 'G E'. But checking: G-A-T-E at 0-1-2-3, so *(p+3)='E'. The option shows 'G T' - p points to G, p+2 would be T. Re-reading: *(p+3) for "GATE" is 'E'. None match exactly - assuming typo in original, output is G E, closest is option A if E shown as E not T.
Consider a function void modify(int *x) { *x = 20; } called as modify(&y). What happens?
A
y is passed by value; changes don't affect original y
B
Address of y is passed; changes inside modify affect original y
C
y is copied to a temporary variable
D
The function cannot access y
Correct Answer:
B. Address of y is passed; changes inside modify affect original y
When &y is passed to a function expecting a pointer parameter, the address is passed. Changes via pointer dereference affect the original variable.
In pointer to function declaration: int (*ptr)(int, int); which statement is correct?
A
ptr is a function returning pointer to int
B
ptr is a pointer to a function taking two ints and returning int
C
ptr is an array of function pointers
D
ptr cannot be used to call functions
Correct Answer:
B. ptr is a pointer to a function taking two ints and returning int
The parentheses around *ptr indicate ptr is a pointer. It points to a function that takes two int parameters and returns an int.
What will be the output?
A
1
B
2
C
3
D
Garbage value
p points to arr[0]. After p += 2, p points to arr[2] which contains value 3. Pointer arithmetic moves by element size.
Which of the following is a valid pointer comparison in C?
A
if(p1 > p2 && p1 < p3) where p1, p2, p3 are unrelated pointers
B
if(ptr == NULL) to check if pointer is null
C
if(p1 == 5) where p1 is a pointer
D
if(p1 - p2 > 10) where p1 and p2 point to different arrays
Correct Answer:
B. if(ptr == NULL) to check if pointer is null
Comparing pointers with NULL is valid. Comparing unrelated pointers or subtracting pointers from different arrays is undefined behavior.
What is the primary issue with this code?
A
Syntax error
B
Pointer p is uninitialized and points to garbage memory
C
The value 10 cannot be assigned through a pointer
D
Missing return statement
Correct Answer:
B. Pointer p is uninitialized and points to garbage memory
p is declared but not initialized to point to any valid memory location. Dereferencing an uninitialized pointer causes undefined behavior.
For dynamic 2D array allocation using int **arr = (int**)malloc(n*sizeof(int*)); what must be done next?
A
Directly assign values to arr[i][j]
B
Allocate memory for each row using a loop
C
Call free() immediately
D
Call realloc() for memory expansion
Correct Answer:
B. Allocate memory for each row using a loop
After allocating memory for pointers, each pointer (row) must be allocated memory individually in a loop before accessing arr[i][j].
Consider the declaration: const int *p; and int * const q;
A
Both p and q cannot be modified
B
p points to a constant integer; q is a constant pointer to integer
C
Both declarations are identical
D
Both p and q can be modified freely
Correct Answer:
B. p points to a constant integer; q is a constant pointer to integer
const int *p means p can change but the data it points to cannot. int * const q means q cannot change but the data it points to can be modified.
What is the output of the following code?
A
10
B
Address of x
C
Address of p
D
Garbage value
q is a pointer to pointer p. **q dereferences q twice: first to get p, then to get the value of x which is 10.
Consider: const int *p; and int * const q; Which statement is true?
A
Both prevent modification of data
B
First prevents pointer change, second prevents data change
C
First prevents data change, second prevents pointer change
D
Both are identical
Correct Answer:
C. First prevents data change, second prevents pointer change
const int *p: pointer can change, data cannot. int * const q: pointer cannot change, data can be modified.
