signed/unsigned byte

[Lamefif]

how can the computer tell the difference between the two?
i mean a byte is 8 bit can be 1 or 0

11111111 = 255 unsigned byte

10000000 = -128 or 128 ?

 

[Bo Persson]

Lamefif wrote:
:: how can the computer tell the difference between the two?
:: i mean a byte is 8 bit can be 1 or 0
::
:: 11111111 = 255 unsigned byte
::
:: 10000000 = -128 or 128 ?

It isn't the byte itself that is different, it is the instructions
used to manipulate it.


Bo Persson

 

[Scott McPhillips [MVP]]

how can the computer tell the difference between the two?
i mean a byte is 8 bit can be 1 or 0

11111111 = 255 unsigned byte

10000000 = -128 or 128 ?

Different programming is used for signed and unsigned. The assembly
language of the processor typically provides two kinds of branch
instructions. For unsigned data a branch opcode checks the carry flag
(which is kind of like a 9th bit after an arithmetic operation). For signed
checks another branch opcode checks the sign bit, which is the 8th bit of
the byte. That is why C++ has both signed and unsigned types: It affects the
code that is generated to test arithmetic results.

 

[Victor Bazarov]

how can the computer tell the difference between the two?

An object of 'signed char' type is signed. An object of
'unsigned char' type is unsigned. An object of type 'char'
is signed or unsigned depending on the implementation.

i mean a byte is 8 bit can be 1 or 0

11111111 = 255 unsigned byte

It's -1 on two's complement, if treated as signed.

10000000 = -128 or 128 ?

It depends on how you look at it.

0x34562ef9 - a long or a float?

V

 

[Lamefif]

Thanks all