Val Does Not Work on Zero

[Alex]

If I use the Val function it works with numbers 1-9. However, if I use "Val" on a 0, it fails.

Code: Select all

A$="0"
If Val(A$)
  PrintN("Found Value")
Else
  PrintN("Is this a bug?")
EndIf

I'm using 3.94 with Slackware Linux

[PB]

> I'm using 3.94 with Slackware Linux

Your code, as it stands, also fails on PureBasic v4.00 Beta 9 for Windows, but
that's because you're not using it correctly. You're supposed to do it like so:

Code: Select all

A$="0"
If Val(A$)=0
  Debug ("Found Value")
Else
  Debug("Is this a bug?")
EndIf

In other words, you're supposed to test the value that Val returns, which you
didn't do. What you're doing is just testing it for True (non-zero) or False (zero).
However, Val doesn't return just True or False, it returns the value of the string.

[Alex]

Your code, as it stands, also fails on PureBasic v4.00 Beta 9 for Windows, but that's because you're not using it correctly. You're supposed to do it like so:

I'm afraid you're not correct. Val behaves differently if I do this:

Code: Select all

A$="1"
If Val(A$)
  PrintN("Found Value")
Else
  PrintN("Is this a bug?")
EndIf

than if I do this:

Code: Select all

A$="0"
If Val(A$)
  PrintN("Found Value")
Else
  PrintN("Is this a bug?")
EndIf

So it reports success in turning 1-9 into a number, but it reports failure turning 0 into a number, which means I can't use Val as a test because I can successfully test the numerals from 1-9 with Val, but if I try to test 0 it fails to test correctly. Thus:

Code: Select all

A$=(a string that might translate into a number)
If Val(A$) ; something IS a number
  Gosub Deal_With_Numbers
Else
  Gosub Deal_With_Strings
Endif

doesn't work. If Val can report success turning strings of 1-9 into numbers, it should be able to report success in turning the string "0" into a number.

Alex

[gnozal]

If Val can report success turning strings of 1-9 into numbers, it should be able to report success in turning the string "0" into a number.
Alex

Val() is not an IsNumber() function. It just converts a string to a number. And like in most basic dialects, Val("NotANumber") = 0 (not a bug).

[Fred]

Val("0") will return 0, which is false in condition.

[blueznl]

However, Val doesn't return just True or False, it returns the value of the string.

yep, and in pb logic 0 = false, and <> 0 = true

[Psychophanta]

Your code, as it stands, also fails on PureBasic v4.00 Beta 9 for Windows,

Sorry but not agree.

but that's because you're not using it correctly.

Again, not agree.

[Fred]

If Val("0") is exactly like the following code, or i miss something ?

Code: Select all

If 0
  Debug "Never show"
EndIf

[Psychophanta]

@Alex;
Why don't you use the "Coding questions" Section for this topic instead of "Bug reports" one?
I can't understand a thing!

[Kale]

One thing to remember about an 'If' statement is that it tests for a true value, not necessarily a number. It just so happens that all numbers in Purebasic other than '0' are considered 'True'.

His code was good code.

Code: Select all

A$="0"
If Val(A$)
  Debug "this is shown when the 'If' finds a true value (a number that is not 0)"
Else
  Debug "this is shown when the 'If' finds a false value (a number equal to 0)"
EndIf

Debug #True
Debug #False 

EDIT: changed my poor code, lol

[Alex]

His code was good code.

Code: Select all

A$="0"
If Val(A$)
  Debug "this is shown when the 'If' finds a true value (a number)"
Else
  Debug "this is shown when the 'If' finds a false value (a number that is not 0)"
EndIf 

Debug #True
Debug #False

Do I have a fundamental misunderstanding of how "If" operates? When I test, is "If" looking at the true/false result, or the result of the operation? Try the following code:

Code: Select all

A$="9"
If Val(A$)
  Debug "this is shown when the 'If' finds a true value (a number)"
Else
  Debug "this is shown when the 'If' finds a false value (a number that is not 0)"
EndIf 

Debug #True
Debug #FALSE
Debug RESULT=Val(A$)

The debugger return appears as follows:

Code: Select all

this is shown when the 'If' finds a true value (a number)
-1
0
9

So there is a difference between the value and result. That is, Val(A$) returns a value of true, (expressed as "not zero,"). It also expresses the operation's result, expressed as the numeral "9"

So it looks like "If" is looking at the true/false value, not the result of the operation, and it appears to distinguish between the two. If "If" was looking at the result of the operation, "#TRUE" would equal "9," unless some internal translation was happening.

But with the same code, if A$=0, I get the following debugger return:

Code: Select all

this is shown when the 'If' finds a false value (a number that is not 0)
-1
0
0

So it looks like "If" is looking at the numerical result, and not the true/false value.

Which of the two is "If" looking at, and how many sets of values are there? It seems to me that there should be two pieces of information returned for every operation - the "true/false" value and the "result" of the operation - a number, string, array, or whatever. As I see things, "If" should access the true/false value. Can you straighten me out?

Thanks,

Alex

[Alex]

Val("0") will return 0, which is false in condition.

Maybe I'm unclear on the concept. Shouldn't Val() (or any other operation) return two pieces of information; a true/false value AND a result, and shouldn't "If" look at the true/false value rather than the result?

Does Val("0") give a value of "true" AND a result of "0" which are kept in separate places? Or does it put BOTH the result and true/false value in the same place?

Alex

[Kale]

Lol! I think i made a typo. This is how it should read:

Code: Select all

A$="0"
If Val(A$)
  Debug "this is shown when the 'If' finds a true value (a number that is not 0)"
Else
  Debug "this is shown when the 'If' finds a false value (a number equal to 0)"
EndIf

Debug #True
Debug #False 

anyway, the main point is that an 'If' in purebasic will test for a true value ONLY. If the result of any expression or value that follows this 'If' keyword so happens to be a '0' (zero) then it is determined to be false. Otherwise it is true.

This allows you to do stuff like:

Code: Select all

If OpenWindow(....)
    ...
Endif

because the return value from 'OpenWindow' should be a handle and if not '0' it must of been successful.

All commands that return a value in PB if they are non-successful they always return a '0' (false).

[dagcrack]

about logic on errros... if equals 0 or is less than 0 its an error, else its not an error. Even if PB does not use negative values as error, many do (I do as well). Just saying though

Code: Select all

a = 0;

If a <=0
  Debug "oops!"
Else
  Debug "meh!"
EndIf

no? - It sure is slower than checking if it equals 0 ... But... depends on the lib you're using, some return negative values.


Tip for newcomers: Never say "you're not right" to Fred, after all, he made what you're using, behave, respect, shut-up and listen to him .

[Kale]

No. Any number other than '0' is true, even negative numbers.

Code: Select all

If -1
  Debug "this is shown when the 'If' finds a true value (a number)"
Else
  Debug "this is shown when the 'If' finds a false value (a number that is not 0)"
EndIf