C Practice Question (Self Designed)

Question

What will be the output of the following program? 

#include <stdio.h>

int main() {
    int i[] = {1,2,3}, j[] = {1,2,3};
    int *p=i,*q=j;
    while ((*p++ = *q++) != 3) {  
        printf("%d", *p);
    }
    return 0;
}

 

Comments

(*p++ = *q++)

((*p)++) = ((*q)++)

With-in a sequence point, *p updated twitce. So, this should be a undefined behaviour.

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@Shaik Masthan isn't *p updated only once (assignment) and p updated once (increament) in one sequence point, as ++ have higher precedence then derefrence operator

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Ohh... My mistake ! You are right.

then output will be 2 and 3 without comma.

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@Shaik Masthan thanks for your response

Answer 1

*p++ = *q++ first copies the value from j to i, then both pointers move to the next element.
The while condition checks the assigned value, not the next one.

After each assignment, p already points to the next element, so printf("%d", *p) prints that next value.

• Assign 1 → p moves → prints 2

• Assign 2 → p moves → prints 3

• Assign 3 → condition fails → loop stops

Output: 23

Comments

it will print 23