Please explain this strange behavior

[oasis375]

$foo = "hello"
If $foo = 0 Then ConsoleWrite("wrong")

It took me some time till I found the mistake in AutoItScript code.

First I assing a value to the variable, then I check if the variable is 0, and the result is positive.

Other version:

$foo = 0 ;default value
;some processing here
    $foo = "hello" ;assignment by process
;end of process
If $foo = 0 Then ConsoleWrite("process failed") ;final check to know process result

 

[Melba23]

oasis375,

When you use comparison operators AutoIt automatically converts then arguments to numbers - and as "hello" converts to 0 you find that the comparison is true. What you need to do is when comparing strings is to use the == operator which forces both sides to string format:

$foo = "hello"
If $foo == 0 Then ConsoleWrite("wrong")

And to prevent the next question of "Why does AutoIt do this", it is a result of using non-typed variables - this was an early design decision by Jon to make AutoIt easy to use which does, at times, cause problems if not properly understood.

M23

[AutID]

Edit: Melba23 types faster!

 

You are comparing a string to a number. I don't even know why this is allowed in autoit but again, this is autoit.
Anyway if you want to compare if the string is equal to an string 0 then use double =.

$foo = "hello"
If $foo == 0 Then ConsoleWrite("wrong" & @LF)

If you want to check if your string is not empty then do it like this:

$foo = "hello"
If $foo <> "" Then ConsoleWrite("wrong" & @LF)

Edited October 25, 2014 by AutID

[Melba23]

AutID,

 

You are comparing a string to a bool

Not so - 0 is a number, booleans are True/False. But your suggested solution is correct.

M23

[AutID]

AutID,

 

Not so - 0 is a number, booleans are True/False. But your suggested solution is correct.

M23

Again you are faster, I corrected that. Confusion!