is integer

You can finding a decimal in a number by using IndexOf function like this:
Dim strvalue As String = "6.8"
If strvalue.IndexOf(".") >=0 then
Messagebox.show "It's a decimal value"
end if

There may be a function just for doing that, but here's the solution that comes to mind first:

Dim l as long = 5.6
if l - CInt(l) = 0 then msgbox("l is an integer") else msgbox("l is not an integer")

In other words, cast it to an integer and subtract that from the original value to see if there is anything left over.

Another way:

        Dim number As Decimal = 6.8
 
        If number - Decimal.Truncate(number) <> 0 Then
            Stop ' Fractional number 
        End If

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