Question

It’s been a while since I start programming in C, however, I still feel confused about unsigned. If we compiled this code:

#include <stdio.h>

int main(int argc, char **argv)
{
    unsigned int x = -1;

    return 0;
}

both gcc and VC++ don’t raise any error or even a warning regarding using negative number with unsigned.

My question is that does unsigned do any internal job or it just a hint to the programer that this value shouldn’t be negative?

Answer 1

It is NOT just a hint. The following two snippets should behave differently:

Signed int:

int x = -1;
printf("%d\n", x > 0);  // prints 0

Unsigned int:

unsigned int x = -1;
printf("%d\n", x > 0);  // prints 1

And you could probably come up with 5 more examples where the signedness matters. For example, shifting right with the >> operator.