# negative representation

Harvinder Singh

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Posts: 90

posted 12 years ago

//1byte b= 0000 0000//ouput is Zero

//2byte b1=1000 0000//compiler error casting is required

//3byte b3=byte(1000 0000)//-128

question: 0 and -128 are both in the range then why the casting is required.

if u have few extra minutes then do tell me how we represent -ve numbers in binary.2's complement is ok but I make a lot of mistakes when I try to do that manually.particularly in substracting binary numbers.thanks

//2byte b1=1000 0000//compiler error casting is required

//3byte b3=byte(1000 0000)//-128

question: 0 and -128 are both in the range then why the casting is required.

if u have few extra minutes then do tell me how we represent -ve numbers in binary.2's complement is ok but I make a lot of mistakes when I try to do that manually.particularly in substracting binary numbers.thanks

Hard work beats talent<br />when talent doesn't work hard.<p> - Tim Notke

Corey McGlone

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Posts: 3271

posted 12 years ago

If you use a literal value, such as 10000000, the compiler automatically interprets that as an int. Therefore, 10000000 isn't the binary version of -128, it's 10,000,000, which certainly doesn't fit into a byte. Check out the JLS, §3.10.1 Integer Literals for more information.

As far as representation of values in 2's complement, here's the easiest way I know to perform the conversion:

Let's say you want to get the binary equivalent to -73. First, get the binary value of it's absolute value, 73. The binary equivalent of 73 is:

01001001

Now, flip the bits:

10110110

Finally, add 1:

10110110 + 1 = 10110111

So, the binary representation of -73 is 10110111.

I hope that helps,

Corey

As far as representation of values in 2's complement, here's the easiest way I know to perform the conversion:

Let's say you want to get the binary equivalent to -73. First, get the binary value of it's absolute value, 73. The binary equivalent of 73 is:

01001001

Now, flip the bits:

10110110

Finally, add 1:

10110110 + 1 = 10110111

So, the binary representation of -73 is 10110111.

I hope that helps,

Corey

Shafkat Talli

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Posts: 30

Corey McGlone

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Posts: 3271

posted 12 years ago

The binary equivalent of 127 is 01111111.

The leftmost bit is a "sign bit." If it's a 0, the number is positive, if it's 1, the number is negative.

Check out this campfire story. You'll find a lot of good information there. Also, if you're confused, do some searches in this forum.

Originally posted by Shafkat Talli:

If this is -128, what is 127 then ? i thought this was 127 ??? now i dont get it anymore.

1000 0000)//-128

The binary equivalent of 127 is 01111111.

The leftmost bit is a "sign bit." If it's a 0, the number is positive, if it's 1, the number is negative.

Check out this campfire story. You'll find a lot of good information there. Also, if you're confused, do some searches in this forum.