MadeEasy Test Series: Programming & DS - Programming In C

Question

Consider the following c-program:

#include<stdio.h>

int main() {

char *arr[ ] ={"GATE", "CAT", "IES", "IAS", "PSU", "IFS" };

call(arr);

return 0;

}

void call (char **ptr) {

char **ptr1;

ptr1=(ptr+=size of (int)) -2;

printf("%s\n",*ptr1);

}

which of the following represent the output of the above program?(Assume size of int,pointer is 4B).

A)IES

B)IAS

C)CAT

D)PSU

Comments

Yes you can add integer to pointer, but it will not be the direct integer that will be added.

Suppose ptr++ => ptr=ptr+1 

it will calulated as ptr=address_pointing_by_ptr+ sizeof(ptr)*1 isn't this correct?

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Yes, it is correct.

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sizeof (char) = 1B

sizeof (int) = 4B

ptr1 = (ptr+= sizeof(int))-2;

let's solve inside () first,

(ptr+= sizeof(int))

ptr was pointing to first element of array but now incremented to 4B and now is pointing to 5th element of array which is "PSU"

so now we got,

ptr1 = (&(arr[4]))-2;

ptr1 will subtract 2B from ptr which is pointing to arr[4] and will point to arr[2]

ptr1 is pointing to arr[2] and will print "IES"

Answer 1

char *arr[ ] ={"GATE", "CAT", "IES", "IAS", "PSU", "IFS" };

Above is a array of character pointers.

Size of a char* = 8 bytes ( normally in a 64-bit system )

let arr = 1000, then arr +1 = 1008 and arr + 2 = 1016

ptr1=(ptr+=size of (int)) -2;

sizeof( int ) = 4

ptr += 4, ptr = ptr + 4, ptr = 1000 + (4*8); ( 8 is the size of character pointer )

ptr = 1032

ptr1 = 1032 - 2 => ptr = 1032 - (2*8) => ptr = 1016

ptr == (arr + 2)

So, 

printf("%s\n",*ptr1)

prints " IES " ( third element of the array )

Comments

**ptr, **ptr1 and *arr are the double pointers. The pointer arithmetic you did it is apply on the single pointer (correct me if i am wrong). in array all the element have size 5,4,4,4,4,4 byte of blocks (Note: different block size). the pointer **ptr, **ptr1 will point to these blocks. But you are taking one level up and doing calculation. How it is relate to the answer?

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*arr is not double pointer it is array of pointers.

Answer 2

This is my approach to solving it please tell if I am wrong