Here's a quick and simple program you can use to learn to convert text to a double, store the double, and return true or false based on the results of the conversion. First, the form:
Standard Form:
Error Form:
The Code
Here's the complete background code:
Public Class Form1
Private dTotal As Double
Private Sub ExitToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExitToolStripMenuItem.Click
Me.Close()
End Sub
Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
If (Not ConvertToMoney(txtAmount.Text)) Then
lblError.Visible = True
Else
lblError.Visible = False
End If
lblOutput.Text = FormatCurrency(dTotal)
End Sub
Private Function ConvertToMoney(ByVal sAmt As String) As Boolean
Try
Dim dResult As New Double
dResult = CDbl(sAmt)
dTotal += dResult
Return True
Catch ex As Exception
Return False
End Try
End Function
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
lblOutput.Text = FormatCurrency(dTotal)
End Sub
Private Sub txtAmount_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles txtAmount.KeyDown
If (e.KeyValue = Keys.Enter) Then
btnAdd_Click(sender, e)
End If
End Sub
End Class
Basically, there's a function you can use to format currency called (oddly enough) FormatCurrency(). All I've done is created a wrapper function that accepts a string, converts it to a double through the use of CDbl(), adds it to a global double total variable, and return true. If any of that fails, I return false. Back in the calling method (btnAdd_Click()), I check the result and display my error message if it returns false. Then I can safely use FormatCurrency() on my total amount.
Code will be up soon.