Binary Subtraction Explained

[MrGreenface]

Thank you for explaining this subject so clearly (and casually). Took me a bit to learn this from reading other resources, but this video helped to clear up any confusion I've had! :)

[jocsoncedrick]

DON'T MAKE IT SO COMPLICATED

[jocsoncedrick]

NO OFFENSE BUT IT SOUNDS CONFUSING BECAUSE OF YOUR VOICE...

[rockpickable]

why do computer scientists keep messing up halloween and christmas?

because 31 (oct) = 25 (dec) !

[jakeycool8899]

@rockpickable I bet this is really clever but my twelve year old brain doesn't understand.

[rockpickable]

@jakeycool8899 there are a couple systems we use to express values. the one that pretty much everybody uses is the decimal (dec) system. the numbers are 1,2,3,4,5,6,7,8,9,10 and then you just keep counting. there also is the octal (oct) system. it only counts 1,2,3,4,5,6,7,10 and then you keep counting that way. just like in binary you count 1,10 the octal system doesnt know the numbers 8 and 9. hope that makes sense :)

[jakeycool8899]

@rockpickable So how does 31 in octal equal 25 in decimal?

[rockpickable]

you just count 1,2,3,4,5,6,7,8,9,10,11,12,13,­14,15,16,17,18,19,20,21,22,23,­24,25 (25 dec)

1,2,3,4,5,6,7,10,11,12,13,14,1­5,16,17,20,21,22,23,24,25,26,2­7,30,31 (31 oct)

its the same value (same amount of different numbers)

[Zoidmatrix]

All your vids are awesome, dude.

I want yout to continue those cool stuff! :D

[Annapolisdweller123]

with negative #s could you just not revert the sign bit?

[greenwolf52]

Just asking but how do computers tell when they are dealing with a new number or if it's part of the number or a sign?

[scjoiner]

@greenwolf52 That's a good question. In my experience, they always just use the highest bit for the sign.

[PieLover5000]

You are so smart and amazing and I didnt really comprehend anything you just said :D

[austo25]

its funny that 240p made the sound bad

[austo25]

he did 010 lol

[Andersmithy]

I was half expecting you to do a quick thing on nines compliment. I guess it wasn't needed though, you did a good job explaining it. Keep up the good work!

[chemdork123]

Nice job, Stephen. I was able to follow your lesson and did not know about 2's complement before. I would have recommended a nice use of color in this video though. For example, it would have helped to make things even easier to understand if you made the sign bit a different color than the value bits (as it might be represented in a textbook). I use color whenever possible when I am giving lessons to students (don't do that anymore so much...).

[62namennaj]

If you find this confusing, wait till you see division

[mariosunshinefaan]

i'm a dummie

[TheMcDucky]

This is just as awesome as minecraft! (Maybe more)

[Radical011Y]

What would you do if you were subtracting a negative number eg 5-(-4) would it be the same?

[Vossenmans1995]

@Radical011Y 5-(-4) = 5+4

[Radical011Y]

@Vossenmans1995 I knew that genius, i was wondering how to calculate it through binary ad whether it was the same method.

[scjoiner]

@Radical011Y The point is that we don't have a real "subtraction button" in computers, we just use this method to fake it.

[chemdork123]

@Radical011Y The way I understand it, you would set it up as 0 / 101 (+5) minus 1 / 100 (-4), where the bit to the left of / is the sign bit. Following 2's complement, 1 / 100 would become 0 / 011 after inversion, then 0 / 100 (+4) after adding 1. Add them together and the answer you get is 0 / 1001, which is (+9). Am I correct, Stephen?

[Radical011Y]

@chemdork123 So you take the twos complement for (-4) then add together? I thought it would something like that just wanted to make sure the process i was doing was correct. I wasnt sure whether id need to take twos complement for (-4) then take it again for 5-4

[chemdork123]

@Radical011Y I believe that should be how it is done... especially since you arrive at the correct answer! Basically if you want to do X-Y, you take the 2's complement for Y, then solve for adding X to that number. If you keep track of the sign bit, it should work itself out pretty clearly.  Again - also the first time I'm really seeing the 2's complement, so I trust that Stephen (or someone else) would readily point out if I was wrong... This is the internet after all. :)

[scjoiner]

@chemdork123 You're right, dude. Thanks for jumping in! Comments don't show up for me unless they are addressed to me.

[TheMattgician]

@Radical011Y Remember, subtracting a negative number is the same as adding.

[xXaceliteXx]

thanks stephen :) ur vids are a big help

[GasparXR]

It's good that you make those tiny mistakes sometimes, because it reminds us that despite all the evidence, you are a human like us and in fact not our own computer teaching us base-2 maths.

[invinciblemode]

The wikipedia page wasn't helpful.

[IPlayInBeastMode]

Stephen doesn't know how to computer.

[swainer25]

Great job this REALLY helps

But could u do a really quick vid on how u make ur vertical rs nor latch

Tbks

[invinciblemode]

I felt dumb when I tried this with decimals. -_-

[GasparXR]

at 12:00 you could also invert it and then add 1, it will give the same number. You probably knew that though :P

[HansLemurson]

@GasparXR

It's cool how the "arithmetic negation" algorithm operates the same way when going Pos->Neg and Neg->Pos

[KartikSPradeepan]

Oh god :( Grade 9 comp sci all over again

[MceeGreen23]

you are amazing

[GasparXR]

Oh snap

[Katalliaan]

Great job explaining it. You videos are making me want to build a redstone calculator with 7-segment displays.

[yandamie]

<3 Where have you been all our lives Stephen?

[Mpa12120]

Yay u released this!!!

[TheMHMproductions]

Can you repeat that?

[zomgbeast97]

not first

[Majoolwip]

2nd



[scjoiner]

240p MLG!

[78monkeymonk]

1st viewer!!!!