very basic question

[priya selva]

how to represent -ve numbers in binary...
eg
x=6;
~x=-7

i know that x= 0000....0110
~x=1111....1001(how do v interpret this as 7)

[Dave Vick]

Priya
To use your number as an example:
7 in binary is
00000000 00000000 00000000 000000111
to get a negative number you flip all of the bits (turn all of the 1s into 0s and all of the 0s into 1s) then add 1 to the result.
To change 7 into -7:

  
00000000 00000000 00000000 000000111   7
11111111 11111111 11111111 111111000   flip all the bits
11111111 11111111 11111111 111111001   add 1

So, the binary number 11111111 11111111 11111111 111111001, is the same as -7 in decimal.
Does that help?

[Greg Ostravich]

There's a Cat and Mouse game with Bits on JavaRanch you may want to check out.
It's easiest to flip the bits and add one to get a negative number.
Here's another way to look at it.
If you substract the highest bit from the rest and negate it.
I'm rusty on bits but here's some examples:

For -1
1111 1111 = -1
128 - 127 = 1
For your 7 example:
0000 0110
1111 1001 8 - 1 = 7
For -10
1111 0110 16 - 6 = 10
For -127
1000 0001 128 - 1 = 127

[ August 14, 2002: Message edited by: Greg Ostravich ]
[ August 14, 2002: Message edited by: Greg Ostravich ]