Solving Conversion Issues: -19210 & -458 in 8 bits

[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

adding 1 gives 01000000₂

the book's answer is 00000010₂

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

the book's answer is 10111011₂

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.

 

[DoctorBinary]

My book is asking for the 2's complement of -192₁₀ and -45₈ in 8 bits.

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.

And I agree with your answer for -45₈.

What book are you referencing?

 

[jofree87]

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

 

[vela]

-45₈

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

flipping the bits and adding 1, I get 11011011₂

the book's answer is 10111011₂

Looks like the book converted -45₁₆.

 

[DoctorBinary]

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

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.