Conversion issue

[Vishy Karl]

Hi all,
I am having a doubt in the questions involving hexadecimal numbers.
i had this question in a mock exam

int ab = 0xFFFFFFFA;
int invertedA = ~ab;

Now how am i supposed to find value of ab which is -6,i mean am is supposed to write
A * 16^0 + F * 16^1 + F * 16^2 and so on ???
i don't think this is the proper way,is there no easier way ? how will i get -6 as the answer.
plz. solve my doubt,
thanks in advance.

[Steve Lovelace]

First, I believe the answer is 5, not -6.
To see how to do the inversion easily, picture what this number looks like in binary. It is:
11111111 11111111 11111111 11111010
Inverting means 1 becomes 0 and vice versa:
00000000 00000000 00000000 00000101
or 101 for short, which is to say 5.

[Jessica Sant]

Originally posted by Steve Lovelace:

11111111 11111111 11111111 11111010
Inverting means 1 becomes 0 and vice versa:
00000000 00000000 00000000 00000101
or 101 for short, which is to say 5.

Don't forget!!! Two's complement means you need to invert the number and then add 1!
So -->

11111111 11111111 11111111 11111010
00000000 00000000 00000000 00000101
+ 1
-----------------------------------
00000000 00000000 00000000 00000110
== 6
So that means it really is -6
But I agree -- the easiest way I've found to convert hex digits is first to convert it to binary then two's complement it (if its negative) and then figure out the decimal representation.

[Dimple Kaushik]

ab=0xFFFFFFFA
in hexadecimal A=10, B=11, C=12, D=13, E=14, F=15
in binary 10,11,12,13,14,15 are 1010, 1011, 1100, 1101, 1110, 1111 resp
so ab = 1111 1111 1111 1111 1111 1111 1111 1010
~ab = 0000 0000 0000 0000 0000 0000 0000 0101 + 1 = 110 = -6

Can anybody tell me how to convert these?
byte a = (byte)127;
byte b = (byte)128;
byte c = (byte)255;
byte d = (byte)256;
//......
System.out.print(a + " " + b + " " + c + " " + d);
Ans: a = 127, b = -128, c = -1, d = 0
Thanks.
[ November 19, 2003: Message edited by: dimple kaushik ]

[Vishy Karl]

Thanks all
Jessica the number given ab is itself -6 according to 2's complement .
then after the operation
int invertedA = ~ab;
it comes to sign change and answer as 5
Thanks all for your answers,
happy preparation,