[ask] About set /a ??

[Fen_Li]

i have read set command help (set /?) more time but i'am not enough understand about "set /a operator" :

i.e. quote from set /?

Two new switches have been added to the SET command:

    SET /A expression
    SET /P variable=[promptString]

The /A switch specifies that the string to the right of the equal sign
is a numerical expression that is evaluated.  The expression evaluator
is pretty simple and supports the following operations, in decreasing
order of precedence:

    ()                  - grouping
    ! ~ -               - unary operators
    * / %               - arithmetic operators
    + -                 - arithmetic operators
    << >>               - logical shift
    &                   - bitwise and
    ^                   - bitwise exclusive or
    |                   - bitwise or
    = *= /= %= += -=    - assignment
      &= ^= |= <<= >>=
    ,                   - expression separator

i not clearly about set /a operator like : |,^,&
anybody can give an example for using bitwise or "|" and bitwise exclusive or "^" on set /a command 



thanks..

[contrex]

How can I convert a decimal number to binary, octal, hexadecimal?

Here is a way to convert a 8-bit decimal to its binary equivalent.
The formulation below emphasizes extracting each bit individually.

   @echo off & setlocal enableextensions enabledelayedexpansion
   set decimal_=%1
   set /a b0=%decimal_% ^& 1
   set /a b1=%decimal_% ^& 2
   set /a b2=%decimal_% ^& 4
   set /a b3=%decimal_% ^& 8
   set /a b4=%decimal_% ^& 16
   set /a b5=%decimal_% ^& 32
   set /a b6=%decimal_% ^& 64
   set /a b7=%decimal_% ^& 128
   set i=-1
   for %%b in (!b0! !b1! !b2! !b3! !b4! !b5! !b6! !b7!) do (
     set bit=%%b
     set /a i+=1
     if !bit! EQU 0 (echo bit !i! = 0) else (echo bit !i! = 1)
   )
   endlocal & goto :EOF


An example of the output
 
   bit 0 = 0
   bit 1 = 0
   bit 2 = 1
   bit 3 = 1
   bit 4 = 0
   bit 5 = 0
   bit 6 = 0
   bit 7 = 0

[Fen_Li]

thanks..it's great...
nice formula..i think

but, i am still not clearly, especially with "^&"
can u give explain that more basicly...
i.e. -->
- set /a "2^3"          ; it return 1
- set /a "3^4"          ; it return 7

what is the meaning of "^" ??
why 2^3=1 (3-2)....and 3^4=7 (3+4) ??

[contrex]

Some confusion because the ^ ("caret") character has 2 purposes...

(1) it is used to "escape" special characters in batch files, especially the & character, which breaks commands otherwise. For example to use a & b in a batch file you must type a ^& b. I know this is confusing but you just have to learn it if you need to do batch arithmentic!

(2) In batch arithmetic the ^ character is also the "bitwise exclusive or" operator.

A bitwise exclusive or takes two bit patterns of equal length and performs the logical XOR operation on each pair of corresponding bits. The result in each position is 1 if the two bits are different, and 0 if they are the same.

You can perform it manually like for school arithmetic as I shall demonstrate:-

Place an 0 in the answer if the bits are the same and a 1 if they are different

2 =      00000010
3 =      00000011
         --------
result = 00000001 = 1

3 =      00000011
4 =      00000100
         --------
result = 00000111 = 7

QED




       

[Fen_Li]

hmmm...
yea, like a logical arithmetic lesson in school ...(maybe in Junior High School)
it's long time ago...


littte mind about logical arithmetic
but, it an OR "|" operator..not XOR

[expression 1] or [expression 2] = Result
if expression 1 is true and expression 2 true , result will be True
if one of expression is False , result will be False

ilustrate on table:

----------------------
A    B          A or B
----------------------
T    T              T
T    F              F
F    T              F
F    F              F

note: T=True , F=False

is this same think as your demonstration ??

[contrex]

is this same think as your demonstration ??

similar idea.

[Fen_Li]

thanks so far for solved my problem...
that's great help...

maybe, I will do some trial an error....to enhance experience..
coz, 'experience is the best teacher'

Regard...