for loop with step increment of 0.1

  • Thread starter Thread starter choi4u
  • Start date Start date
C

choi4u

Running this code
Sub test()
For i = 1.5 To 2 Step 0.1
Debug.Print i
Next i
End Sub

gives this output
1.5
1.6
1.7
1.8
1.9 .

Why does the output not include 2.0?
and what do I have to do to make the output include 2.0?

Thanks in advance.
 
To add to thos ecomments try this

Sub test()
Dim i As Single
For i = 1.5 To 2 Step 0.1
p = i + 0.1 > 2
Debug.Print i
Debug.Print p
Next i
End Sub

As you will note as soon as i = 1.9 then i + 0.1 is greater than 2 (True) so
it never executes.

Mike
 
I'd guess that there was an internal rounding problem that you got hit with.

I'd use:

Sub test()
Dim i As Long
For i = 15 To 20 Step 1
Debug.Print i / 10
Next i
End Sub
 
The problem has to do with floating point representation and the inability
of VB (actually, any language) of being able to store all fractions in a
given integer data type (the problem is akin to the decimal representation
of 2/3, a decimal point followed by an unending string of 6's, invariably
the number is written as a fixed number of 6's followed by an ending 7)...
whatever has accumulated in the loop variable "i" at the 1.9 stage, adding
0.1 to it gives a number ever so slightly greater than 2 which is outside of
the ending loop limit, hence the loop ends at the 1.9 value. The way around
this problem is to not use floating point numbers. For example...

Sub test()
For i = 15 To 20
Debug.Print i / 10
Next i
End Sub

(note the modified loop limits) where whenever you would have used "i" in
your original loop code, you would use "i/10" instead.

Rick
 
Running this code
Sub test()
For i = 1.5 To 2 Step 0.1
Debug.Print i
Next i
End Sub

gives this output
1.5
1.6
1.7
1.8
1.9 .

Why does the output not include 2.0?
and what do I have to do to make the output include 2.0?

Thanks in advance.
Click to expand...

It's due to the age old binary to decimal conversion problem.
Computers use binary representations of real numbers that often (most
often) do not convert exactly to their decimal equivalents without
some remainder. This leads to the commonly occurring problem that you
see here.

As Dan Guillett suggested, one workaround is simply increase the end
value to compensate for the error, though I might use 2.01 to keep
from confusing the issue more - that is, "Why isn't 2.1 in the list?"
Another approach might be to convert the loop from a FOR to a Do Until
with a Round function to correct for the error ...

Sub test()
step = 0.1
i = 1.5
Do Until i > 2
Debug.Print i
i = Round(i + step, 1)
Loop
End Sub

Another way that would work is to round the index in the FOR loop ...

Sub test()
For i = 1.5 To 2 Step 0.1
Debug.Print i
i = Round(i, 1)
Next i
End Sub

Tom Lavedas
===========
http://members.cox.net/tglbatch/wsh/
 
Back
Top