Re: [users] Bug in Rnd function (StarBasic)?

[Johnny Andersson]

Hi!
I always bought that one until I tried it myself. The reason why 1.0 never  
occurs in your modification of my code, is that you modified a > to a <...

My code:
If Value>0.99999 Then
   Count1=Count1+1
   If Value=1 Then
      Count2=Count2+1
   Endif
EndIf
Your code:
If Value<0.99999 Then
   Count1=Count1+1
   If Value=one Then
      Count2=Count2+1
   Endif
EndIf
The inner IF statement (If Value=one Then...) will never be executed since  
Value can never be 1.0 if Value<0.99999...
I corrected the < to a > and executed it again. The result was:

"Rnd>0.99999 occured 22 times, Rnd=1 occured 22 times. This was calculated  
in 130 s."

So still, no values between 0.99999 and 1.0 occured since all 22 times  
when Rnd>0.99999, Rnd was 1.000000...

Sorry for being such an annoying person...
Best regards
Johnny

Andrew Douglas Pitonyak <[EMAIL PROTECTED]> skrev den Fri, 20 May 2005  
15:51:55 -0400:

I changed your code and recieved a very different answer. Consider the  
following:

Sub RndTest0
    Dim i As Long
    Dim Count1 As Long, Count2 As Long
    Dim Value As Double
    Dim one As Double
    Dim ExecTime As Long
    one = 1.0
    ExecTime=Timer
    Randomize
    For i=1 To 1000000
        Value=Rnd
        If Value<0.99999 Then
            Count1=Count1+1
            If Value=one Then
                Count2=Count2+1
            Endif
        EndIf
    Next i
    ExecTime=Timer-ExecTime
    Print "Rnd>0.99999 occured "+Count1+ _
          " times, Rnd=1 occured "+Count2+ _
          " times. This was calculated in "+ExecTime+" s."
End Sub
Note: I used type Long rather than Integer to avoid round off.
Second, I did not compare to "1", which is an integer, but rather, I  
stored 1.0 in a variable and compared to that. I could have also  
compared against "1.0". This version NEVER returns a value of 1.0.

Johnny Andersson wrote:
I found that the Rnd function returns values (0.00000... to  
1.00000...),  not (0.00000... to 0.99999...), which would be better in  
most cases.

Example:
Dim MyInteger As Integer
Dim MyArray(1 To 6) As Integer
Randomize
MyInteger=Int(6*Rnd)+1 'Supposed to return numbers 1 to 6, byt may now  
and  then return 7. Happened to me many times.
MyArray(MyInteger)=MyArray(MyInteger)+1 'Causes an error message if   
MyInteger>6 which may happen in this case.

In this example Rnd returns 1.
Sub RndTest
    Randomize 30091
    Print Rnd
End Sub
This example took about 2 minutes to run on my PC (450 MHz P2, a few  
other  applications were running at the same time):

Sub RndTest0
    Dim i As Long
    Dim Count1 As Integer, Count2 As Integer
    Dim Value As Double
    Dim ExecTime As Long
        ExecTime=Timer
    Randomize
    For i=1 To 1000000
        Value=Rnd
        If Value>0.99999 Then
            Count1=Count1+1
            If Value=1 Then
                Count2=Count2+1
            Endif
        EndIf
    Next i
    ExecTime=Timer-ExecTime
Print "Rnd>0.99999 occured "+Count1+" times, Rnd=1 occured "+Count2+"   
times. This was calculated in "+ExecTime+" s."
End Sub

It seems like every time Rnd>0.99999 then Rnd=1, so even though Rnd   
produces 15 decimals it seems like only 5 (or less) are relevant. When  
I  tried Rnd=1 at 20 to 34 occasions (different result different times  
of  course) which indicates that Rnd=1 about once every 29000 to 50000  
times.

Anyway, is Rnd=1 supposed to ever happen or is this a bug?
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