Why is minus one (-1) equal to true in VB again?

[Ruffin Bailey]

I coulda sworn I was given an explanation during an AppDev class years
ago for VB6, but don't recall the answer. Why is it that -1 is True
in Visual Basic (and now VB.NET)? Bit flags seem like they should
always be 0 or 1 to me... (not that I haven't used VB long enough by
now to know better).

Sorry to pester, but "why is -1 = true?" is a difficult thing to
Google!

Ruffin Bailey

[One Handed Man \( OHM - Terry Burns \)]

Acording to the help file . . .

Boolean variables are stored as 16-bit (2-byte) numbers

HTH

--

OHM ( Terry Burns )
. . . One-Handed-Man . . .
"Herfried K. Wagner [MVP]" <hi************ ***@gmx.at> wrote in message
news:2j******** *****@uni-berlin.de...

* ka****@mailinat or.com (Ruffin Bailey) scripsit:

I coulda sworn I was given an explanation during an AppDev class years
ago for VB6, but don't recall the answer. Why is it that -1 is True
in Visual Basic (and now VB.NET)? Bit flags seem like they should
always be 0 or 1 to me... (not that I haven't used VB long enough by
now to know better).

Booleans are stored as 32-bit-integers.

'False' = 000000....000 (BIN) = 0 (DEC)
'True' = 111111....111 (BIN) = -1 (DEC)

The first bit is the sign bit, if it's set to 1 that indicates a
negative number.

--
Herfried K. Wagner [MVP]
<URL:http://dotnet.mvps.org/>

[Herfried K. Wagner [MVP]]

* "One Handed Man \( OHM - Terry Burns \)" <news.microsoft .com> scripsit:

Acording to the help file . . .

Boolean variables are stored as 16-bit (2-byte) numbers

You are right ;-).

--
Herfried K. Wagner [MVP]
<URL:http://dotnet.mvps.org/>

[One Handed Man \( OHM - Terry Burns \)]

This code disassembly appears to store the value '0' for False, if you
assign True to 'v' then the ldc.i4 line becomes ldc.i4.1.

So it would appear that in actual fact the binary storage for this type is
actually False=0 and True=1.

This seems to be converted differently when expressing as numeric types.

// Code size 5 (0x5)
.maxstack 1
.locals init ([0] bool v)
IL_0000: nop
IL_0001: ldc.i4.0
IL_0002: stloc.0
IL_0003: nop
IL_0004: ret
} // end of method Form1::Button1_ Click

--

OHM ( Terry Burns )
. . . One-Handed-Man . . .
"Herfried K. Wagner [MVP]" <hi************ ***@gmx.at> wrote in message
news:2j******** *****@uni-berlin.de...

* "One Handed Man \( OHM - Terry Burns \)" <news.microsoft .com> scripsit:

Acording to the help file . . .

Boolean variables are stored as 16-bit (2-byte) numbers

You are right ;-).

--
Herfried K. Wagner [MVP]
<URL:http://dotnet.mvps.org/>

[Mythran]

Think about it...when you use numbers in VB w/o conversion, what data type is 1?
Integer. So, how many bytes does an integer use? In this case, you have an
integer value so converting that to binary as Herfried described now, because of
the compliment, also turns on the sign bit. Understand???

Mythran

Hi Herfried,

This is how it is done for a boolean you need only one bulb which can be on
and off.
(or one bit in a computer)

:-)

Cor

Booleans are stored as 32-bit-integers.

'False' = 000000....000 (BIN) = 0 (DEC)
'True' = 111111....111 (BIN) = -1 (DEC)

The first bit is the sign bit, if it's set to 1 that indicates a
negative number.

[One Handed Man \( OHM - Terry Burns \)]

This code disassembly appears to store the value '0' for False, if you
assign True to 'v' then the ldc.i4 line becomes ldc.i4.1.

So it would appear that in actual fact the binary storage for this type is
actually False=0 and True=1.This code disassembly appears to store the
value '0' for False, if you

This seems to be converted differently when expressing as numeric types.

// Code size 5 (0x5)
.maxstack 1
.locals init ([0] bool v)
IL_0000: nop
IL_0001: ldc.i4.0
IL_0002: stloc.0
IL_0003: nop
IL_0004: ret
} // end of method Form1::Button1_ Click

--

OHM ( Terry Burns )
. . . One-Handed-Man . . .
"Mythran" <ki********@hot mail.com> wrote in message
news:ex******** ******@tk2msftn gp13.phx.gbl...

Think about it...when you use numbers in VB w/o conversion, what data type is 1? Integer. So, how many bytes does an integer use? In this case, you have an integer value so converting that to binary as Herfried described now, because of the compliment, also turns on the sign bit. Understand???

Mythran

Hi Herfried,

This is how it is done for a boolean you need only one bulb which can be on and off.
(or one bit in a computer)

:-)

Cor

Booleans are stored as 32-bit-integers.

'False' = 000000....000 (BIN) = 0 (DEC)
'True' = 111111....111 (BIN) = -1 (DEC)

The first bit is the sign bit, if it's set to 1 that indicates a
negative number.

[Cor Ligthert]

Hi OHM,

The correct answer is in my opinion given by Greg Young.

What you than take as value is not important as long as true not is 0.

Cor

[Herfried K. Wagner [MVP]]

* "One Handed Man \( OHM - Terry Burns \)" <news.microsoft .com> scripsit:

This code disassembly appears to store the value '0' for False, if you
assign True to 'v' then the ldc.i4 line becomes ldc.i4.1.

So it would appear that in actual fact the binary storage for this type is
actually False=0 and True=1.

This seems to be converted differently when expressing as numeric types.

// Code size 5 (0x5)
.maxstack 1
.locals init ([0] bool v)
IL_0000: nop
IL_0001: ldc.i4.0
IL_0002: stloc.0
IL_0003: nop
IL_0004: ret
} // end of method Form1::Button1_ Click

Sure, 'False' is always 0, and 'True' is something <> 0. When doing a
'Not' on a 'Boolean' set to 'False' it's -1 because that's the complement of 0
interpreted as a signed short.

--
Herfried K. Wagner [MVP]
<URL:http://dotnet.mvps.org/>

[One Handed Man \( OHM - Terry Burns \)]

My point was that true is not stored as -1, rather that it is stored as 1.
Which is different to what every one was saying. It is only when you convert
it that it to a numeric type that it becomes Minus 1.

--

OHM ( Terry Burns )
. . . One-Handed-Man . . .
"Cor Ligthert" <no**********@p lanet.nl> wrote in message
news:Oh******** ******@TK2MSFTN GP12.phx.gbl...

Hi OHM,

The correct answer is in my opinion given by Greg Young.

What you than take as value is not important as long as true not is 0.

Cor

[Herfried K. Wagner [MVP]]

* "One Handed Man \( OHM - Terry Burns \)" <news.microsoft .com> scripsit:

My point was that true is not stored as -1, rather that it is stored
as 1.

It's stored as -1 if you do a 'Not False'.

--
Herfried K. Wagner [MVP]
<URL:http://dotnet.mvps.org/>

[Larry Serflaten]

"Ruffin Bailey" <ka****@mailina tor.com> wrote

I coulda sworn I was given an explanation during an AppDev class years
ago for VB6, but don't recall the answer. Why is it that -1 is True
in Visual Basic (and now VB.NET)?

Because the logical operators were always bit-wise operators.

That meant And, Or, Xor, and Not, could be used on numbers
as well as boolean conditional expressions.
7 And 3 = 3

if (2>0) And (4>2) then ...
It was an industry standard that False equaled 0, but what
value would satisfy these statements;

? = Not 0

0 = Not ?
The Not operator is just a bit-wise complement operator,
as it always had been, but because of that, there is only
one value that can be plugged into the statements above.

0 is a number where all bits are set to 0, so that means
its complement is a value whose bits are all set to 1.
In 2's complement notation (the format used to store signed
values in memory) a value with all its bits set to 1 equates
to -1.

LFS