How to round and truncate long decimal strings in vb.net for compact framework

Earlier today I asked this question:

I will have string data coming in, with 1, 2, or 3 digits preceding the decimal point, and 12 digits after the decimal point.  An example would be 12.918171615141.  I need to truncate everything past the 4th decimal digit, so that my example string would look like 12.9181.

Better yet would be if I could ROUND it properly, so that in this example I would end up with 12.9182.  But to do so, I assume I would have to move the string to a numeric variable and use a math function.  IF this is feasible, I need some sample code to handle this as well, i.e. how to properly get it into a numeric variable, then do the rounding, and get it back in to a string.  TIA

And the most complete answer I got was this:

Dim yv as Double

if Double.TryParse(strABC, out yv) then
     'strABC a valid decimal.
     yv = Math.Round(yv, 3, MidpointRounding.AwayFromZero)
     strABC = yv.ToString()
else
    yv = nothing
end if

I closed out the question too soon, because now that I'm able to try this code, I am getting syntax errors.  I suspect that some of this may be because I'm working in the compact framework environment with its limitations.  Unfortunately I failed to mention this in my earlier question.

Specifically, here are the errors I am getting:

1) In the line that says "if Double.TryParse(Me.txtLocTot.Text, out yv) then", it is saying that "TryParse is not a member of Double", and "name out is not declared", and "comma or valid expression expected" at the end of that line.

2) In the line that says "yv = Math.Round(yv, 3, MidpointRounding.AwayFromZero)", it says "MidpointRounding is not declared".

I have messed with it for quite a while, but getting nowhere.  So, any suggestions to will be appreciated.  TIA
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sasllcAsked:
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Fernando SotoRetiredCommented:
Hi sasllc;

The following code is working on my box but could not Test on Compact framework but should work on it as well.

Dim yv As Double 

if Double.TryParse(strABC, yv) then
     yv = Math.Round(yv, 4, MidpointRounding.AwayFromZero)
     strABC = yv.ToString()
else
    '' If the string could not be converted to a double it returns a zero in yv but it that is not expectable 
    '' make it some negative value.
    yv = -1
end if

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sasllcAuthor Commented:
The syntax errors I get are these:

'TryParse' is not a member of 'Double'.

Name 'MidpointRounding' is not declared.

Any idea how to get around these two problems?  I am using Visual Studio 2008, developing for a mobile device.
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Fernando SotoRetiredCommented:
I have VS 2013 and tried it on a project using mobile device template and it does compile. I tried looking for documentation but could not find anything specific to mobile api support. I do not know if I will be of any help with this issue.
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