I need help with my homework!

[Disconn3cted]

I am supposed to "Evaluate these expressions where A is 11111110 and B is 00000010 using two’s complement."

A+B=?
-B=?

I know how to add binary numbers but I don't know what two's compliment is and my book doesn't give a book explanation on how this relates to arithmetic.

I know 11111110 + 00000010 = 100000000 but I found a website that has the answers to all of the questions in this assignment and the answer is supposed to be 00000000. I'm totally lost, please help me. I don't want the answers. I really want to know how to solve this...

[chickenfeather]

http://en.wikipedia.org/wiki/Two%27s_complement

[Disconn3cted]

http://en.wikipedia.org/wiki/Two%27s_complement

-edit-

Nevermind, maybe I was over thinking this.

[Smi!ezZ]

11111120
and
-10

=]

[Disconn3cted]

11111120
and
-10

=]

[Razorhead]

My solution:
It's been over a year since I made my last 2-complement's calculation ><

Spoiler!

in two complement's:
11111110 = -2 = A
00000010 = 2 = B
(-2) + 2 = 0 = A+B
00000000 = 0 = A+B


B = 2
so
-B = -2

00000010 = 2
11111110 = -2 (126-128 = -2)

If the most significant bit is 1: '7-bit value' - 128 = 'correct value'
I only remember the 'easy' way (converting to decimals ><)

[CrimsonNuker]

Dayum. What class is this?

[Disconn3cted]

Dayum. What class is this?

It is "Introduction to computer science" or Computer Science 111.

I think I figured it out. Two's compliment is used to represent a negative binary number. All the ones and zeros are reversed and then one is added to it. The directions confused me because it sounded like two's compliment was necessary for solving all of them and it wasn't.

[CrimsonNuker]

Lawl. I'm in gr 12 computer science (ICS4U), and I've never done anything like this, all we do is program shit

[BlackFox898]

Lawl. I'm in gr 12 computer science (ICS4U), and I've never done anything like this, all we do is program shit

lol same, even the same course code (ICS4U). our teacher is going to teach us C++, but all hes been doing is talking about SDLC and company structure

[CrimsonNuker]

Lawl. I'm in gr 12 computer science (ICS4U), and I've never done anything like this, all we do is program shit

lol same, even the same course code (ICS4U). our teacher is going to teach us C++, but all hes been doing is talking about SDLC and company structure

Everybody I know from other schools are learning C++, but our teacher is making us finish up Visual Basic from ICS3U, then we're moving on the Adobe Flex Builder...

[EvGa]

Speaking of CS homework here's a problem I'm having trouble with right now...

Read in a text file with the first int declaring 2D array size and then two coordinates (3,0) and (1,3). The coordinates correspond to components in the array. Using a northeast path, ie the ability to move up or right, find and print out all possible paths to the finish cord.

So, from a 5 by 5 2D array, print out all possible paths from (3,0) to (1,3), only allowed up or right movements.

Do this using only recursion. <---- FML

In java. <---- FML


It's due tomorrow. <---- FML

I've been working on this shit for 4hrs now, I waited until the last day thinking I had it all planned out in my head.. failed when I went to actually code it. I blow at recursion, give me loops any day. Going to be an all-nighter.



EDIT:

[Aiyas]

Man, did this stuff back when I took Computer Arithmetic(over 3 years ago...)