CODEWITHSUNDEEP
cmacosoperandnegation
csjr
csjr

Reputation: 136

C operand ~and a char

I would like to know what the ~ operand does with a char. Example code: the output is -1 if var="a". 

int ret (char var)
{
   int x;
   x=var|~var;
   return x;
}
int main()
{
  printf("%d",ret("a"));
  return 0;
}

I dont understand why it returns -1

Upvotes: 2

Views: 312

Answers (2)

David C. Rankin
David C. Rankin

Reputation: 84569

The ~ operator is the negation operator which has the identity -x-1. There is both a logical (bitwise) negation and an arithmetic negation. C implements an arithmetic negation with the ~. Take for example x=5in binary:

x = 5

The the ~ operation would have the following effect:

~x = -5-1 = -6

In your case 'a' is 97 or 01100001, therefore

~a = -97-1  (or -98)

Sorry for the confusion

Upvotes: 1

emesday
emesday

Reputation: 6186

First "a" and 'a' are different. "a" passes the address of string array "a" and 'a' passes the char a. So you need to modify the code as

printf("%d",ret('a'));

Once modified, var is 97 which is 0x00000061 and ~var is -98 which is 0xffffff9e.

0x00000061 | 0xffffff9e will be 0xffffffff that will be '-1' by Two's complement.

If you want 0xffffffff, use %x instead as

printf("0x%x",ret('a'));

Upvotes: 2

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