Compare unsigned with signed (int and short) in C

Question

Hello i have tried to understand the output of the following code in C but i dont get why x is x greater than y i.e why is x > y?

#include <stdio.h>

int main(){
   short a = -2;
   unsigned short b = -a;
   int x = -2;
   unsigned y = -x;

   if(a<(unsigned short)b)
       printf("a < b\t");
   else
       printf("a >= b\t");

   if((unsigned)x<y)
       printf("and x < y\n");
   else
      //my problem is here
       printf("and x >= y\n");
}

output : a < b and x >= y

`x` is not `> y` because `x` is negative. But `x` cannot be cast to `unsigned` without changing its value in some way. You basically told the compiler to ignore the fact that `x < 0` and use some other value, which will follow its type conversion rules. — Weather Vane, Jun 20 '21 at 15:41
To `<` compare a _signed_ with _unsigned_: `a < 0 || (unsigned) a < b`. — chux - Reinstate Monica, Jun 20 '21 at 15:51

score 1 · Accepted Answer · answered Jun 20 '21 at 15:43

1

If you run this program:

#include <stdio.h> 
int main(void){
   short a = -2;
   unsigned short b = -a;
   int x = -2;
   unsigned y = -x;

   printf("a = %hd\n", a);
   printf("b = %hu\n", b);
   printf("x = %d\n", x);
   printf("y = %u\n", y);
   printf("(unsigned)x = %u\n", (unsigned)x);
   if(a<(unsigned short)b)
       printf("a < b\t");
   else
       printf("a >= b\t");
   if((unsigned)x<y)
       printf("and x < y\n");
   else
       printf("and x >= y\n");
}

the answer will be obvious. Why (unsigned)x is such a big number. It is because the x is a two's complement number. -2 in this format is 0xfffffffe

answered Jun 20 '21 at 15:43

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`(unsigned short)b` does not change the type of `b` as it is `unsigned short`. So why cast? Just echoing OP's code? – chux - Reinstate Monica Jun 20 '21 at 15:52
@chux-ReinstateMonica I did not even notice that. Just added the `printf`s. You would notice that before not very fortunate @AbhilekhGautam edit – 0___________ Jun 20 '21 at 16:00

Compare unsigned with signed (int and short) in C

1 Answers1