Geek asks and answers

In C, how can you check if a bit is set using XOR?

I asked this question in an interview. Suppose I have to check bit 3 for:

 a=0x9004;

I said that

 if((a<<13>>15)^1==1)
     printf("bit 3 is not set");
 else
     printf("bit 3 is set");

But I feel that this is not what they were looking for.

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3 answers
if ((unsigned int )a ^ (0x4) < (unsigned int )a) 
    printf("bit 3 is set");
else
    printf("bit 3 is not set");

If bit 3 ( 0x4) was set, then there a ^ 0x4will be less arithmetic value, then a.

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if((a | (1<<2)) ^ a)
   printf("3rd bit is not set");
else printf("3rd bit is set");
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as requested only with XOR. bit starts from 0 to bit 31.

#include <stdio.h>
//assuming you count from bit 0, bit 1,bit 2 up to bit 31..
int main(void){

int a = 0x7FFFFFFF;
int check = (1<<3);
check = (a - (check^a) )>0 ? 1:0;
printf("bit 3 of %x is set to %d",a,check);
return 0;
}
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