Ngọc Duy - 1 year ago 86
Vb.net Question

# How to use the Compute to calculate the total with Double Datatype

I have expression string:

``````dim str as string = "999999999 * 999999999"
``````

I use DataTable.Compute to calculate:

``````dim dt as new datatable
dim result as double = 0
result = cdbl(dt.Compute(str))
``````

And I get an error:

``````Value is either too large or too small for Type 'Int32'.
``````

How can I control result datatype in this case?

Solution:

This function work like Windows's Calculator. Code so confuse but it work :)

``````'input = "999,999,999 x 888,888,888 + 112,365 ÷ 15 − 987,653"
Public Shared Function strCalc(ByVal input As String) As String
If input.Substring(input.Length - 1, 1) = " " Then input = input.Substring(0, input.Length - 3)
input = input.Replace("−", "-").Replace("x", "*").Replace("÷", "/").Replace(",", "")
Dim temp As Double = 0
Dim arr() As String = input.Split(" ")

If arr.Length > 1 Then
temp = New DataTable().Compute(If(arr(0).Contains("."), arr(0), arr(0) & ".0") & " " & arr(1) & " " &
If(arr(2).Contains("."), arr(2), arr(2) & ".0"), "")
If arr.Length > 3 Then
For i As Integer = 3 To arr.Length - 1 Step 2
temp = New DataTable().Compute(temp & " " & arr(i) & " " &
If(arr(i + 1).Contains("."), arr(i + 1), arr(i + 1) & ".0"), "")
Next
End If
Return temp
End If
Return input
End Function
``````

Runtime is treating your expression "999999999 * 999999999" as a multiplication of two integer values and trying to return it as an object which is the return type of Compute API. The output of multiplication of those numbers is resulting in a very large value which is crossing the maximum value which can be stored in a variable of int (System.Int32) data type. It results in arithmetic overflow exception. To give a hint to the runtime so that it considers the expression as a multiplication of two `double` numbers please use following code:
`dim str as string = "999999999.0 * 999999999.0"`