Why is this program ignoring the Values field? - vb.net

Question

Structure WeightElement
Dim LowPointer As Integer
Dim HighPointer As Integer
Dim TraitPointer As Integer
Dim Values As WeightedTrait()
Dim Num As Integer
End Structure
Structure WeightedTrait
Dim TraitName As String
Dim TraitNum As Integer
Dim WeightValue As Decimal
End Structure
Function DefaultWeights()
Dim Weight(39) As WeightElement
Weight(0).LowPointer = 1
Weight(0).HighPointer = 2
Weight(0).Num = 5
Weight(0).Values = DefaultValues({"Black", "White", "East Asian", "South Asian", "Middle Eastern"}, {26, 30, 27, 28, 29})
Return Weight
End Function
Function DefaultValues(NameArray() As String, NumArray() As Integer)
Dim Weight(NameArray.Length) As WeightedTrait
For x = 0 To NameArray.Length - 1
Weight(x).TraitName = NameArray(x)
Weight(x).TraitNum = NumArray(x)
Weight(x).WeightValue = 1
Next
Return Weight
End Function
Sub Main()
Dim Query As String = ""
Dim Weight() As WeightElement = DefaultWeights()
For x = 0 To 38
Query += Str(Weight(x).LowPointer)
Query += ","
Query += Str(Weight(x).HighPointer)
Query += ","
Query += Str(Weight(x).TraitPointer)
Query += ","
Query += Str(Weight(x).Num)
Query += ","
Try
For y = 0 To Weight(x).Values.Length - 1
Query += Str(Weight(x).Values(y).TraitName)
Query += ","
Query += Str(Weight(x).Values(y).TraitNum)
Query += ","
Query += Str(Weight(x).Values(y).WeightValue)
Query += ","
Next
Catch
Query += "FLOCK"
End Try
Query += ";"
Next
Console.WriteLine(Query)
End Sub
The code is supposed to transform a weight into a string, yet when I run it the values in the Values array in the weight is nowhere to be seen. Instead, for some reason it decides to always go down the catch statement, and append that instead. Why won't it acknowledge the Values array?

Answer 1

DefaultWeights() only initializes one WeightElement so only Weight(0).Values is set. Weight(1).Values to Weight(39).Values remain set to Nothing so the Length property is not available and an error is raised.
Note that the most accurate way to find the upper bound of an array is to use the GetUpperBound function. For one-dimensional arrays, the dimension parameter = 0.In this case, the array has been created with the upper bound set to 39 (room for 40 elements). If this size was changed, the Main code would not need to be updated with the new size.
I have also modified the code to only output the Query string if Weight(x).Values has been populated.
Sub Main()
Dim Query As String = ""
Dim Weight() As WeightElement = DefaultWeights()
For x = 0 To Weight.GetUpperBound(0)
Try
If Weight(x).Values IsNot Nothing Then
Query += CStr(Weight(x).LowPointer)
Query += ","
Query += CStr(Weight(x).HighPointer)
Query += ","
Query += CStr(Weight(x).TraitPointer)
Query += ","
Query += CStr(Weight(x).Num)
For y = 0 To Weight(x).Values.GetUpperBound(0)
Query += ","
Query += CStr(Weight(x).Values(y).TraitName)
Query += ","
Query += CStr(Weight(x).Values(y).TraitNum)
Query += ","
Query += CStr(Weight(x).Values(y).WeightValue)
Next
Query += ";"
End If
Catch
Query += "FLOCK;"
End Try
Next
Console.WriteLine(Query)
End Sub