why -n is ture?

[rbhkamal]

Why negative values evaluate as true in the following:

if -1 then
;kill self
 endif

Was this always the case? Or did the behavior change at some point?

Edited April 3, 2009 by rbhkamal

[YellowLab]

I don't know if this has always been the case, but I would assume yes. Usually, only 0=FALSE all other values = true.

Bob

[GEOSoft]

Why negative values evaluate as true in the following:

if -1 then
;kill self
 endif

Was this always the case? Or did the behavior change at some point?

It returns True because it is True

$iVal = -1
If $iVal = -1 Then
   MsgBox(0, "Results", "It's True")
Else
   MsgBox(0, "Results", "It's False")
EndIf

[rbhkamal]

I understand that AutoIt treats -1 as true... I discovered it the hard way. But it doesn't make sense; negative values are almost always an error in all languages. What is the logic behind this behavior?

[trancexx]

I understand that AutoIt treats -1 as true... I discovered it the hard way. But it doesn't make sense; negative values are almost always an error in all languages. What is the logic behind this behavior?

Logic is this:

-1 is not nothing

[Jos]

I understand that AutoIt treats -1 as true... I discovered it the hard way. But it doesn't make sense; negative values are almost always an error in all languages. What is the logic behind this behavior?

You have 2 options being True or False. 0 = False, anything else is True.

Doesn't that make sense?

Jos

[GEOSoft]

I understand that AutoIt treats -1 as true... I discovered it the hard way. But it doesn't make sense; negative values are almost always an error in all languages. What is the logic behind this behavior?

-1 does equal -1 therefore it is true. What can be simpler than that? As has been stated Only 0 or an empty string ("") are false when looking at the value of variables. I think what you want would be a new function like Boolean() where only positive values resolve to True

[rbhkamal]

Logic is this:

-1 is not nothing

I see... thanks

[Edit] Thanks everyone...

Edited April 3, 2009 by rbhkamal

[GEOSoft]

Actually if you want another test then try this one and see the difference.

$iVal = -1
If NOT $iVal Then
   MsgBox(0, "Results", "It's False")
Else
   MsgBox(0, "Results", "It's True")
EndIf

That's why the keyword NOT is there

[rbhkamal]

Actually if you want another test then try this one and see the difference.

$iVal = -1
 If NOT $iVal Then
    MsgBox(0, "Results", "It's False")
 Else
    MsgBox(0, "Results", "It's True")
 EndIf

That's why the keyword NOT is there

Thanks

[Ascend4nt]

A value of 'True' typically represents -1 or 1 in a language. -1 is the same as all bits set.

Here's what MSDN says:

The encoding for logical FALSE is all bits set to zero (0x0), and the encoding for logical TRUE is all bits set to 1 or 0xFFFF

http://msdn.microsoft.com/en-us/library/cc...0(PROT.10).aspx

[Richard Robertson]

True and false are relative. The easiest difference is false equals zero and true equals non zero. That's how most processors run anyways. There are checks for things like "if the value in some register or on the top of the stack equals zero, branch {here}."

[Ascend4nt]

I'm not sure how other processors work, but for the Intel chipsets, there are no built-in 'bool' types/operations or 'If variable' logic tests, unless you count the 'cx' register and its 'jcxz' instruction - but that itself requires the register to first contain the data you'd like to test. (which in the case of most variables requires a 'mov' to cx first). There are conditional jumps\operations based on a 'zf' (zero-flag), but these must be preceded by a compare or 'test' operation. To emulate 'If' tests in higher-level languages, you would either use 'test' to test if certain/all bits are set, or compare a value to zero (which logically is the same as 'If x=0' or 'If x<>0'). Also, using 'not' would be the equivalent of changing a value's status from true to false (no-bits set to all-bits set and vice versa).

So basically, no - the processor doesn't run the same way as 'If variable' logic statements work. That is something you will only find in higher-level languages, which themselves can use any set of machine instructions they like, though the easiest would be 'cmp [var],0'.

[Richard Robertson]

Who was that comment directed at?