GATE CSE 2017 Set 2 | Question: 55

Question

Consider the following C program.

#include<stdio.h>
#include<string.h>
int main() {
    char* c="GATECSIT2017";
    char* p=c;
    printf("%d", (int)strlen(c+2[p]-6[p]-1));
    return 0;
}

The output of the program is _______

Comments

Please note here that you don’t really need to remember the ASCII values of T or I. Why?

Because you just have to know the number of alphabetical difference between the two characters T & I. The difference is simply 11 (you can even count it on your fingers). Assuming A → 1; B → 2; C → 3;….. Z → 26

I.e; what’s the difference between G & D ?
‘G’ – ‘D’:   7 – 4 = 3

This intuition would come in handy in the exam environment.

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Key concepts to note:

1. 2[p] = *[p+2] = p[2]
2. 6[p] = *[p+6] = p[6]

%s of (c+10) is 17, strlen in int will be 2.

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assume starting address as 100

100+(84-73-1)=100+10=110

after which two characters are there resulting in the length of 2.

Answer 1

2 is the answer.

Comments

@MiNiPanda @Shaik Masthan

when pointer subtraction is directly allowed then why here we are subtracting ASCII value why not address?

 

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2[p] or 6[p] are not pointers, those are elements

Answer 2

Easiest method:

c + 2[p] -6[p] -1
= c + p[2] –p[6] -1
= c + T – I – 1
= c + 11 -1
= c + 10
strlen(17) = 2

Source: https://www.geeksforgeeks.org/gate-cs-2017-set-2-gq/ -- explanation of Q.53

Answer 3

The base of the question was STRLEN doesn’t count NULL byte.

Answer 4

This is a C program that uses pointer arithmetic to calculate the length of a string.

The string "GATECSIT2017" is stored in a character pointer variable c. A pointer variable p is also defined and it is assigned the value of the pointer c.

In the printf statement, the expression (c+2[p]-6[p]-1) is used to calculate the length of the string.

The expression c+2[p] is equivalent to c+2[c], which means that it is referencing the 3rd character of the string (index 2) which is 'T'

The expression 6[p] is equivalent to 6[c], which means that it is referencing the 7th character of the string (index 6) which is 'I'

So, the expression c+2[p]-6[p]-1 is equivalent to 'T'-'I'-1 which evaluates to -9.

The printf statement prints the value of this expression as an integer, which is -9.

It is important to note that this code will not give the correct length of the string, as the strlen() function is not used in the program, and the expression used to calculate the length is not correct and it will always return -9.