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GATE CSE 2024 Session 2 Q36: Pointer difference and value difference for a double array

Question

What is the output of the following C program?

#include <stdio.h>
int main() {
    double a[2]={20.0, 25.0}, *p, *q;
    p = a;
    q = p + 1;
    printf("%d,%d", (int)(q - p), (int)(*q - *p));
    return 0;}

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Answer: B (official GATE 2024 final answer key)

Concept used: Subtracting pointers gives a count of elements, not bytes; dereferencing gives the stored values.

First step: q points one element after p, so q − p counts elements; *q − *p is 25.0 − 20.0.

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Source: official GATE 2024 Session 2 CS question paper and final answer key, organised by IISc Bangalore. Question paper · Answer key

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