Visual Basic 2008 New Search Query - vb.net

Question

I'm trying to do a search through an access database I added to a project but I get this error: An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in System.Data.dll"
Additional information: No value given for one or more required parameters.
The idea was to search the database for text entered into a textbox, then display the information on that row within more text boxes.
The code dr = cmd.ExecuteReader is also highlighted as an issue when debugging. I'm using visual basic 2008, and quite new to the whole coding scene so explanations as to why the issue has occurred would be appreciated!
Imports System.Windows.Forms
Imports System.Data.OleDb
Public Class frmSearch
Public con As OleDbConnection = New OleDbConnection
Public dr As OleDbDataReader
Dim dbProvider As String
Dim dbSource As String
Dim BillingSystemFolder As String
Dim TheDatabase As String
Dim FullDatabasePath As String
Private Sub frmSearch_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'TODO: This line of code loads data into the 'BillingdatabaseDataSet.BillingInfo' table. You can move, or remove it, as needed.
Me.BillingInfoTableAdapter.Fill(Me.BillingdatabaseDataSet.BillingInfo)
dbProvider = "PROVIDER=Microsoft.ACE.OLEDB.12.0;"
'Setup the provider
TheDatabase = "/billingdatabase.accdb"
BillingSystemFolder = Application.StartupPath
FullDatabasePath = BillingSystemFolder & TheDatabase
'Set the database and the location of it
dbSource = "Data Source = " & FullDatabasePath
'Set the data source
con.ConnectionString = dbProvider & dbSource
'Set the connection string
End Sub
Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSearch.Click
con.Open()
txtJobNum.Clear()
txtName.Clear()
txtSurname.Clear()
Dim str As String
str = "SELECT * FROM BillingInfo WHERE (Code = " & CodeText.Text & ")"
Dim cmd As OleDbCommand = New OleDbCommand(str, con)
dr = cmd.ExecuteReader
While dr.Read()
txtSurname.Text = dr("Surname").ToString
txtName.Text = dr("First Name").ToString
txtJobID.Text = dr("Customer ID").ToString
End While
con.Close()
End Sub
End Class

Answer 1

Probably the field Code is a text field. In this case when you want to search using a particular value for that field you should enclose the value between single quotes.
Something like this
str = "SELECT * FROM BillingInfo WHERE (Code = '" & CodeText.Text & "')"
However this is really a bad practice because this allows to create an Sql Injection attack or it will simply fail because your value contains a single quote.
The correct method is using a parameterized query like this
str = "SELECT * FROM BillingInfo WHERE (Code = #p1)"
Dim cmd As OleDbCommand = New OleDbCommand(str, con)
cmd.Parameters.Add("#p1", OleDbType.VarWChar).Value = CodeText.Text
dr = cmd.ExecuteReader