GATE CS 2020 Q.32 (CS Q.22): Pointers, Arrays and Strings

Consider the following C program.

#include <stdio.h>
int main() {
    int a[4][5] = {{
        {1, 2, 3, 4, 5},
        {6, 7, 8, 9, 10},
        {11, 12, 13, 14, 15},
        {16, 17, 18, 19, 20}
    }};
    printf("%d\n", *(*(a + **a + 2) + 3));
    return (0);
}

The output of the program is _______.

Your answer

Official answer and solution

Official answer: 19
From: Official GATE 2020 answer key

Solution

Evaluate pointer dereferences and array subscript offsets step by step.

Given array declaration: int a[4][5] = {{1..5}, {6..10}, {11..15}, {16..20}};.

Step 1: Evaluate **a:

a decays to a pointer to its first row a[0] (type int (*)[5]).
*a is the array a[0], which decays to a pointer to its first element &a[0][0] (type int *).
**a = *(*a) = a[0][0] = 1.

Step 2: Evaluate a + **a + 2:

a + 1 + 2 = a + 3.
a + 3 points to the 4th row of the 2D array, which is a[3].

Step 3: Evaluate *(*(a + 3) + 3):

*(a + 3) is the array a[3], which decays to &a[3][0].
Adding 3 gives &a[3][3].
Dereferencing *(&a[3][3]) gives a[3][3].
The 4th row a[3] contains {16, 17, 18, 19, 20}.
Index 0 is 16, index 1 is 17, index 2 is 18, and index 3 is 19.
Thus, the printed output is 19.

Final answer

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2020 Computer Science and Information Technology (CS)
Question: 32 of 65, printed as CS Q.22
Section: Computer Science and Information Technology

Report an error in this question

GATE questions are the work of the organising institutes. This site is independent and is not affiliated with them.

Question

Solution

Source