How to find the Sum or Total of a Listbox - vb.net

Question

I have a listbox that has two columns of date entered into it using the code:
'Press to place value into Array
Private Sub TxtMark_Enter(ByVal sender As System.Object, _
ByVal e As KeyEventArgs) Handles TxtMark.KeyDown
Dim Mark As Double
Dim DataString As String
If e.KeyCode = Keys.Enter Then
If Double.TryParse(TxtMark.Text, Mark) = False Then
MessageBox.Show(" You must enter a numeric value like 1 or 2")
TxtMark.Clear()
TxtMark.Focus()
Exit Sub
End If
If Mark < 0 Then
MessageBox.Show("Valid range is between 0 and 100, 7 would work " _
& Mark.ToString & " Does not")
TxtMark.Clear()
TxtMark.Focus()
Exit Sub
End If
If NumberOfScores < MaxEntries Then
ScoreArray(NumberOfScores) = Mark
DataString = (NumberOfScores + 1).ToString + ". " + _
NameArray(NumberOfScores).PadRight(15) + _
Mark.ToString.PadLeft(5)
Lstdisplay.Items.Add(DataString)
NumberOfScores += 1
End If
TxtMark.Clear()
TxtName.Clear()
TxtName.Focus()
Exit Sub
End If
What I want to do is have a label that does the some of the Mark automatically as the data is entered. Any ideas would be great

Answer 1

The solution is to iterate through all entries and add up the values:
Dim total As Double
For Each s As String In ListBox1.Items
total+= s.substring(...)
Next
Debug.WriteLine("The total is:" + total.ToString)
The tricky part is extracting the numeric value from the string.
But it would be much easier if you placed the data into a ListView control. With the values all in one column. Then you don't need to do the substring to extract the numeric values out

Answer 2

One idea would be to add a custom extension that returns the numeric part of the string and then use Matt Wilko's iteration as above.
To create a custom extension add a class to your project as follows:
Imports Microsoft.VisualBasic
Imports System.Runtime.CompilerServices
Namespace Extensions
Public Module ExtensionMethods
<Extension()> _
Public Function GetNumeric(ByVal source As String) As String
'Takes the passed in string and returns the numeric part
Dim ReturnString As String = ""
For A = 1 To source.Length
If IsNumeric(source.Substring(A, 1)) Then
ReturnString += source.Substring(A, 1)
End If
Next
Return ReturnString
End Function
End Module
End Namespace
If you then import MyProject.Extensions on you project you can use string.GetNumeric to return the numeric part of your code.
Hope this helps you (and others).