CODEWITHSUNDEEP
c
Nishant Kumar
Nishant Kumar

Reputation: 6083

Bitwise negation operator of unsigned int

I am not able to understand why it's output is ffff it should be 0000. Let say int take 2 byte ffff will stored in memory : 1111 1111 1111 1111 so after ~a value will become: 0000 0000 0000 0000. but out put coming ffff am I missing some general concept ?

  #include <stdio.h>
    void main()
    {
      unsigned int a = 0xffff;
      ~a;
      printf("%x", a);
    }

Output : ffff

Upvotes: 0

Views: 1612

Answers (5)

haccks
haccks

Reputation: 106012

In the statement 

~a;

~ operator NOT (complement) the value of a and its value gets discarded (unlike the unary operator ++ and --), i.e, ~a does nothing to a unless you assign it to a 

a = ~a;

Upvotes: 0

Avi Turner
Avi Turner

Reputation: 10456

How about saving the value of the operation:

a = ~a;

You did perform the bitwise ~ operation, but you did not assign the returned value to any variable.
This operator returns a value, and does not modify variable itself.

Upvotes: 1

user1814023
user1814023

Reputation:

You have to assign the value back to the variable. You are just doing ~a. You are not assigning it back to a.

a = ~a;

will give you proper output.

Upvotes: 1

SoulRayder
SoulRayder

Reputation: 5166

you should do 

a = ~a;

to assign the negated value to a.

or if you want to just print it, do 

 printf("%x", ~a);

Upvotes: 5

OmnipotentEntity
OmnipotentEntity

Reputation: 17131

The ~ operator does not change the variable in place, it returns the result of the change. So in order to perform a bitwise negation of a variable you need to assign it to itself:

a = ~a;

Upvotes: 2

Related Questions