GATE CSE 2020 | Question: 22

Question

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 _______.

Comments

Concept:

a = address of 0^th index of 2D array i.e address of 1D array {1,2,3,4,5}.

*a = address of 0^th index element of 0^th index of above array i.e address of first element of array(1)

**a = value of 0^th index element of 0^th index of array above i.e 1.

Similarly (a+3) represents address of 3^rd index of 1-D array, *(a+3) represents address of 0^th index of 3^rd index of 1D array i.e address of 16

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good question on 2 dimensional array ,really enjoyed that

Answer 1

'$a$' is a two dimensional array.

• $a =$ address of $0^{th}$ index of 2-D array which means address of 1-D array
• $^*a =$  address of $0^{th}$ index element of $0^{th}$ index 1-D array
• $^{**}a =$ value at $0^{th}$ index element of $0^{th}$ index 1-D array
  • $\implies ^{**}a = 1$
  • $\implies ^{**}a+2 = 1+2 = 3$
• $a+3 =$ address of $3^{rd}$ index 1-D array
• $^*(a+3) = $ address of $0^{th}$ index element of $3^{rd}$ index 1-D array
• $^*(a+3)+3 =$ address of $3^{rd}$ index element of $3^{rd}$ index 1-D array
• $^*(^*(a+3)+3) =$ value at $3^{rd}$ index element of $3^{rd}$ index 1-D array $= 19$

Correct Answer: $19.$

Comments

for practice : https://gateoverflow.in/254355/test-series-question

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Amazing!

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Easy conversion for these qs: $*(a+i) = a[i]$

Thus, $^*(a+3) = a[3]$

and $^*(^*(a+3)+3) = *(a[3]+3) = a[3][3] = 19$

Answer 2

Answer : 19

a[4] [5] = {{1, 2, 3, 4, 5},

                   {6, 7,8, 9, 10},

                 {11, 12, 13, 14, 15},

                 {16, 17,18, 19, 20}};

Lets solve step-by step :   

step1-   * ( * ( a + ( * ( * a ) ) + 2 ) + 3 )           // note :     ( *(* a)) = 1

step2-    * ( * ( ( (a + 1 )+ 2) ) + 3 )                 

step3-    * ( * ( a + 3) +3)                                // note :    *(a+3)   is address of the memory location where                                                                                                                                           16 is stored or address of 4th row

step4-    * ( * ( a + 3) +3)                                // note. :    *(a+3)+3 now its the address of 4th row and 4th column index.                                                                                                                (a+0) is 1st row so a+3 is 4th row or address of 19

step5-    * ( * ( a + 3) +3)  means value stored at 4th row and 4th column .

so , 19