GATE CSE 2021 Set 2 | Question: 10

Question

Consider the following $\text{ANSI C}$ program.

#include <stdio.h>
int main() 
{
    int arr[4][5];
    int  i, j;
    for (i=0; i<4; i++) 
    ​​​​​​{
        for (j=0; j<5; j++) 
        {
            arr[i][j] = 10 * i + j;
        }
    }
    printf(“%d”, *(arr[1]+9));
    return 0;
}

What is the output of the above program?

• A. $14$
• B. $20$
• C. $24$
• D. $30$

Comments

Row Major Order is used in C Language, therefore the following mapping between logical 2D array to physical 1D memory happens in a C program.

 

 

 

With this idea in mind, We will also note that
 

arr[1] is a pointer to the first element of the 1st row. 

 

To get to arr[1] + 9, we need to follow the row-major order. 

---

24

Answer 1

Answer – Option C

After executing of for loop, Array will be – 

0	1	2	3	4
10	11	12	13	14
20	21	22	23	24
30	31	32	33	34

Now ,

printf(“%d”, *(arr[1]+9));

arr[1] means address of first integer of second row ( as Index starting from 0)  . arr[1]+9 = arr[1]+9*sizeof(int) 

 

i.e arr[2][4] element which is 24

Answer 2

1. for (i=0; i<4; i++)
2. ​​​​{
3.     for (j=0; j<5; j++)
4.      {
5.        arr[i][j] = 10 * i + j;
6.       }
7. }
8. After execution of the code array is stored as :

9. 0	1	2	3	4
   10	11	12	13	14
   20	21	22	23	24
   30	31	32	33	34

   coming to this line :printf(“%d”, *(arr[1]+9));

10. In one dimensional array arr[1] means the second element in the array .Because array index index is start from 0.

11. But in two arrays arr[1] means it is pointing to 2^nd row of containing 5 integer elements

12. → in 2D array ,rows addresses are represented as :

13. 1^st row address means *(arr+0)

14. 2^nd row address means *(arr+1)

15. 3^rd  row address means *(arr+2)   and so on…

16. arr[1]+9 means *(arr+1)+9*(sizeof integer),here it is pointing to the arr[2][4] ,

17. because after 9 elements of the first row is arr[2][4] and count start from 0^th element of the first row.

18. *(arr[1]+9)=*(*(arr+2)+4) it means the element which contains in that address i.e arr[2][4] =24

Answer 3

The question asked us to find *(a[1] + 9 ) .

a[1] refers to the 2nd row of the matrix and *(a[1]) refers to the first element of the 2nd row of the matrix , so we have to find the element after 9 positions after the first position of the 2nd row of the matrix .

Hence the answer comes to be 24