GATE CS 2019 Q.34 (CS Q.24): Pointers, Arrays and Strings

Consider the following C program:

#include <stdio.h>
int main(){
    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 5}, *ip = arr + 4;
    printf("%d\n", ip[1]);
    return 0;
}

The number that will be displayed on execution of the program is ___________.

Your answer

Official answer and solution

Solution

Trace pointer arithmetic and array indexing in C.

We are given the array:

int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 5};

The element indices and values are:

The pointer ip is initialized as:

int *ip = arr + 4;

Here, ip points to element arr[4] (value 5).

The expression ip[1] is equivalent by definition to *(ip + 1):

\text{ip}[1] = *(\text{arr} + 4 + 1) = *(\text{arr} + 5) = \text{arr}[5]

The value of arr[5] is $6$ . Therefore, printf displays $6$ .

Final answer

Common trap

Printing arr[4] (5) instead of arr[4 + 1] (6).

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