GATE CS 2021 Set 2 — Question 20
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Programming & Data Structures → C Programming → Arrays & Strings in C
Last updated
Question
Consider the following ANSI C program.What is the output of the above 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;
}
Correct answer
(C) 24
Solution
The program declares a 2D array
arr[4][5] and initializes it using the formula arr[i][j] = 10*i + j.The expression to be printed is *(arr[1] + 9).1.Understanding
arr[1]: In C, arr is a 2D array. arr[1] decays to a pointer to the first element of the second row, i.e., it points to arr[1][0].2.Pointer Arithmetic: C stores 2D arrays in row-major order (contiguous memory). Adding an integer to a pointer moves it forward by that many elements of the type it points to (here,
int).-
arr[1]points to the element at row index 1, column index 0. - Adding 9 moves the pointer 9 positions forward in the contiguous memory block.
- The array has 5 columns.
-
arr[1][0]is at logical index in a flattened view. -
arr[1] + 9points to logical index . - To find the row and column for index 14: (row index) and (column index).
- So,
*(arr[1] + 9)accessesarr[2][4].
- The value is initialized as
10*i + j. - For
i=2, j=4: .
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