# confused about the “~” operator

Preety Narashimhan

Greenhorn

Posts: 28

posted 14 years ago

Was a little bit confused about the “~” operator. Please clarify.

Consider this eg:

3 is represented in the binary form in this manner

00000000 00000000 00000000 00000011

When we say ~3 we invert the “0” bits to “1” right?

So it becomes

11111111 11111111 11111111 11111100

which when converted into decimal becomes :

………+16+8+4+0+0

right? And since the last higher bit is “1” it is a negative number.

Then how is ~3 = -4??? What is the binary format of –4??

I feel

00000000 00000000 00000000 00000100 = 4

10000000 00000000 00000000 00000100 = -4

Is this rite?

Please correct me if I am wrong.

Consider this eg:

3 is represented in the binary form in this manner

00000000 00000000 00000000 00000011

When we say ~3 we invert the “0” bits to “1” right?

So it becomes

11111111 11111111 11111111 11111100

which when converted into decimal becomes :

………+16+8+4+0+0

right? And since the last higher bit is “1” it is a negative number.

Then how is ~3 = -4??? What is the binary format of –4??

I feel

00000000 00000000 00000000 00000100 = 4

10000000 00000000 00000000 00000100 = -4

Is this rite?

Please correct me if I am wrong.

Thomas Paul

mister krabs

Ranch Hand

Ranch Hand

Posts: 13974

posted 14 years ago

Nope. Negative numbers are stored in twos compliment form.

00000000 00000000 00000000 00000100 = 4

11111111 11111111 11111111 11111011 = swap all the digits

11111111 11111111 11111111 11111100 = now add 1

And that's how negative numbers are stored.

00000000 00000000 00000000 00000100 = 4

11111111 11111111 11111111 11111011 = swap all the digits

11111111 11111111 11111111 11111100 = now add 1

And that's how negative numbers are stored.

Associate Instructor - Hofstra University

Amazon Top 750 reviewer - Blog - Unresolved References - Book Review Blog

Dirk Schreckmann

Sheriff

Posts: 7023

posted 14 years ago

You may want to take a look at this past conversation on the ~ operator. David posted a nice looking link at the end of it.