Using Double data type in for next loop to search for an unknown value.

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Hi, I am working on a program that tells if me the value (which is unknown to me but I know the range (which is from 0.00000001 To 1.0 is present or not)).

The value is in decimal. I have used the Double data type (not sure if I should be using this data type because I have been using float). The test data I am using in the textbox is:

CSS

invertYMouse:false
mouseSensitivity:0.5
fov:0.0
gamma:0.37323943
saturation:0.0
renderDistance:5
guiScale:0

Here is the code of what I am doing:

VB

For a As Double = 0.00000001 To 1.0

    If TextBox1.Text.Contains("gamma:" + Convert.ToString(a)) Then

        MsgBox("Your value is: " + Convert.ToString(a))
        Exit Sub
    End If

    a = a + 0.00000001
Next

Every time I run my code it simply exits the procedure. Help regarding this would be really appreciated.

Regards,
Ammar Ahmad

Posted 9-Jan-14 9:41am

Ammar_Ahmad

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Ron Beyer · Accepted Answer · 2014-01-09T09:59:00

Solution 1

You need to identify the step, otherwise it just adds one, since .0000001 + 1 > 1.0, it will exit after one loop.

VB

For a As Double = 0.00000001 To 1.0 Step 0.0000001

And get rid of the a = a + ... at the bottom.

[Edit]

Given your example data, here is an easier way to find gamma that doesn't require 37,323,943 loops... Plus your code will miss it if they have an extra decimal place beyond the one you selected.

1. Create a string array.
2. Split the string (using String.Split) to split it based on line (Environment.NewLine).
3. Find the element that starts with "gamma"
4. Split that into 2 strings (using String.Split again), only on the ":" this time.
5. Use Double.Parse to parse the second element of #4 above and get the value.

There is no reason to loop through every possible value looking for a match...

Posted 9-Jan-14 9:59am

Ron Beyer

Updated 9-Jan-14 10:09am

v3

Comments

Maciej Los 9-Jan-14 16:03pm

+5

Ron Beyer 9-Jan-14 16:23pm

Thanks!

CPallini 9-Jan-14 16:22pm

5.

Ron Beyer 9-Jan-14 16:23pm

Thanks!

Matt T Heffron 9-Jan-14 16:24pm

+5 (you beat me to it...)

Ron Beyer 9-Jan-14 16:30pm

Thanks Matt

Ammar_Ahmad 9-Jan-14 17:22pm

Thanks for the fast reply but now I am in another issue. I have a breakpoint in the procedure so I can see exactly how the values in variable are. It seems like the value is never reached. Here is the result:
http://imgur.com/4vGgJ1g

Ron Beyer 9-Jan-14 17:26pm

The Double data type has difficulty hitting very precise numbers, so what you are seeing is an issue in precision. This is why you should not use a loop like this to search for the value. If you want to do this, turn it into a float, but really this will take 37 MILLION loops to find the value you gave for an example. The suggestion I gave you will solve it literally 37 million times faster. I'm not exaggerating.

Ammar_Ahmad 9-Jan-14 17:37pm

Thanks :D that helped a lot :D