result of (X and Y)

Posted on 2002-07-17
Last Modified: 2010-05-02
I am working on a maintenace system which has code which I do not understand,

basically it has:

Public Sub Load(lngOptions As Long)

If (lngOptions And 1) = 0 then
     'Do something
     MsgBox "Got here 1"
End If
If (lngOptions And 2) = 0 then
     'Do something else
     MsgBox "Got here 2"
End If
If (lngOptions And 4) = 0 then
     'Do something
     MsgBox "Got here 4"
End If
If (lngOptions And 32) = 0 then
     'Do something else
     MsgBox "Got here 32"
End If

End Sub

(I have added the message boxes)

So if I have,

Private Sub Command1_Click()
Call Load(1)
End Sub

All but the first msgbox come up but if I have Call Load(10) all but the second 1 will come up.  So basically I am looking for some sort of general Algorithm to determine what the result of (X And Y) where X and Y are Integers.


Question by:damienm
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Expert Comment

ID: 7159243
Do you want to add X and Y together and return the result?  Where are the values of X and Y in the code?

Please give details on exactly what you want to accomplish.
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 7159251
the X AND Y returns the bitwise result, so you have to "see" the integers in their bit representation:

0 -> 00000000
1 -> 00000001
2 -> 00000010
3 -> 00000011
4 -> 00000100
5 -> 00000101
6 -> 00000110
7 -> 00000111
10-> 00001010

10 AND  1 -> 1010 AND 00001 -> 0
10 AND  2 -> 1010 AND 00010 -> 1
10 AND  4 -> 1010 AND 00100 -> 0
10 AND 32 -> 1010 AND 10000 -> 0



Author Comment

ID: 7159254
I want to know if I have e.g.

msgbox (1 And 2)


msgbox (4 And 2)

What will be returned without me having to run the code.

So a general algorithm

for the result of
(X And Y)
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LVL 143

Accepted Solution

Guy Hengel [angelIII / a3] earned 50 total points
ID: 7159290
in fact, my last output was incomplete:

10 AND  1 -> 01010 AND 00001 -> 00000 -> 0
10 AND  2 -> 01010 AND 00010 -> 00010 -> 2
10 AND  4 -> 01010 AND 00100 -> 00000 -> 0
10 AND 32 -> 01010 AND 10000 -> 00000 -> 0

bitwise AND returns a bit set to 1 only if that bit for both input was set to 1, otherwise the result is 0 for that bit.


Author Comment

ID: 7159304
That explains the result although it does not explain why anyone would want to do this.


LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 7159308
the explanation is simply that instead of passing x boolean arguments, you pass 1. The advantage is that if you add another IF( ), you don't need to change the procedure arguments, which can be important for versioning (compatibility).

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