Buscar en un array

HOLA A TODOS, COMO PUEDO HACER PARA K ME BUSQUE UN CODIGO INGRESADO EN MI PROGRAMA Y AL MOMENTO DE BUSCAR ME INDIQUE SI EXISTE O NO EXISTE. DE ANTEMANO GRACIAS - ESTOY TRBAJANOD EN APLICACION PARA WINDOWS

Public Class Form1
Public Shared i As Integer = 0
Dim alum(5) As ListaAlumno.ListaAlumno
Sub agregar()

i += 1
alum(i).codAlum = mtxtCodigo.Text
alum(i).Nombre = txtNombre.Text
alum(i).Apellido = txtApellidos.Text
alum(i).Especialidad = cbEspecialidad.Text

End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub

Private Sub btnAñadir_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAñadir.Click

agregar()
listAlumno.Items.Add(alum(i).codAlum & " " & alum(i).Nombre & " " & alum(i).Apellido & " " & alum(i).Especialidad)
MsgBox("Alumno guardado!", MsgBoxStyle.OkOnly, "OK")

End Sub

Private Sub btnNuevo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNuevo.Click
If i < 5 Then
mtxtCodigo.Text = ""
txtNombre.Text = ""
txtApellidos.Text = ""
cbEspecialidad.Text = ""
Else
MsgBox("Lista llena!", MsgBoxStyle.OkOnly, "OK")
End If
End Sub

Private Sub btnBuscar_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBuscar.Click

For i = 0 To 5
If mtxtCodigo.Text = alum(i).codAlum Then
MsgBox("el codigo existe " & txtBuscar.Text)
Exit For
Else
MsgBox("el codigo no existe " & txtBuscar.Text)
Exit For
End If
Next
End Sub
End Class

ESTO ES MI CLASE:
Public Class ListaAlumno
Public Structure ListaAlumno
Public codAlum As Integer
Public Nombre As String
Public Apellido As String
Public Especialidad As String
End Structure

End Class

Private Sub Command1_Click()
Dim x As Integer
Dim Det() As String
Dim strBuscar As String
Det = Split("dedo,saco,nariz,diamante,rey", ",")
strBuscar = "diamante"
For x = LBound(Det()) To UBound(Det())
If Det(x) = strBuscar Then MsgBox "El String """ & strBuscar & """ está en el elemento " & x _
& " de mi Array", vbInformation, "*PsYkE1*"
Next
End Sub