Cheking duplicate name and insert user vb.net - vb.net

Question

I am doing a form where the user is writing his username and choose from a button list. Before the insert i need to check if the username is already existed or not. The server side code is:
Protected Sub btnSubmit_Click(sender As Object, e As System.EventArgs) Handles btnSubmit.Click
'Duplicate username
Dim username As String = tbUsername.Text.Trim()
Dim tempUser As Byte = CByte(rblDept.SelectedIndex)
Dim query1 As String = "Select cUserName FROM Intranet.dbo.Gn_ISCoordinators WHERE cUserName = #cUserName"
Dim haha As DataTable = New DataTable()
Using adapter = New SqlDataAdapter(query1, ConfigurationManager.ConnectionStrings("IntranetConnectionString").ConnectionString)
adapter.Fill(haha)
If haha.Rows.Count <> 0 Then
lblmessage.Text = "Error! user name is already exist"
Return
End If
End Using
'Insert new user
Dim query As String = "Insert into Intranet.dbo.Gn_ISCoordinators (cUserName,lDeptUser) Values ('" & username & "'," & tempUser & ")"
Dim hehe As DataTable = New DataTable()
Using adapter1 = New SqlDataAdapter(query, ConfigurationManager.ConnectionStrings("IntranetConnectionString").ConnectionString)
adapter1.Fill(hehe)
lblmessage.Text = "User has been added"
End Using
End Sub
So when the user press the button it first check the duplicate username if everything is ok, then it inserts the row.
Btw the error is occur when i press on submit button and it gave me this Must declare the scalar variable "#cUserName". on adapter.Fill(haha) line.
Please i want to know what is wrong with my code. Help me
Thanks in advance.

Answer 1

Error message shows everything you need to know to solve that issue. You're using parameter #cUserName in your query, but it is never set.
Dim conn As New SqlConnection(ConfigurationManager.ConnectionStrings("IntranetConnectionString").ConnectionString)
conn.Open()
Dim query1 As String = "Select cUserName FROM Intranet.dbo.Gn_ISCoordinators WHERE cUserName = #cUserName"
Dim command As New SqlCommand(query1, conn )
Dim param As New SqlParameter()
param.ParameterName = "#cUserName"
param.Value = username
command.Parameters.Add(param)
Using adapter = New SqlDataAdapter(command)

Answer 2

You are using a Parameter #cUserName but you did not initialize it or pass values to it.
Dim conn As New SqlConnection(ConfigurationManager.ConnectionStrings("IntranetConnectionString").ConnectionString)
conn.Open()
Dim query1 As String = "Select cUserName FROM Intranet.dbo.Gn_ISCoordinators WHERE cUserName = #cUserName"
Dim command As New SqlCommand(query1, conn)
command.Parameters.AddWithValue("#cUserName",username)
Using adapter = New SqlDataAdapter(command)