# Homework Help: 2's Complement

1. May 30, 2010

### jofree87

Im having some trouble with these conversions, specifically numbers out of the -127 to 128 range, and numbers with bases that are not 10. My book is asking for the 2's complement of -19210 and -458 in 8 bits. Here is my work.

-19210

19210 = 110000002

(Do I add on another 0 on the left most end here?)

flipping the bits, I get 001111112

how are they getting this?
________________________________

-458

For this I tried using the shortcut method and got 458 = 001001012

flipping the bits and adding 1, I get 110110112

any help?

sorry about posting 2 questions in one thread, I just didn't want to clutter the forum with problems that were so similar.

2. May 31, 2010

### DoctorBinary

Hmm. -192 requires nine bits, unless this is a trick question; but even then, if you assign -192 to a "char" variable in C, the answer is 64, not 2.

What book are you referencing?

3. May 31, 2010

### jofree87

The book is "Engineering Problem Solving with C++" second edition, by Delores M. Etter and Jeanine A. Ingber.

4. May 31, 2010

### vela

Staff Emeritus
Looks like the book converted -4516.

5. May 31, 2010

### DoctorBinary

I used Google Books to find the page with the question -- it didn't say anything about the number of bits required (you said 8). I couldn't find the page with the answer, but if it's what you said it is, I don't see how it's right.

I think vela is right about -4516.

Maybe you should look for an errata or try to contact the authors.