Public Class Form1
 
    Private codeMessages As Dictionary(Of Integer, String)
 
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) _
      Handles Button1.Click
        codeMessages = New Dictionary(Of Integer, String)
        Dim csvFilePath As String = "D:\test.csv"
 
        Using stream As New System.IO.StreamReader(csvFilePath, _
          System.Text.Encoding.Default)
            Do
                Dim currentLine As String = stream.ReadLine
                Dim charIndex As Integer = currentLine.IndexOf(";")
                Dim codeValue As Integer
 
                If Integer.TryParse(currentLine.Substring(0, charIndex), _
                  codeValue) Then
                    If Not codeMessages.ContainsKey(codeValue) Then
                        codeMessages.Add(codeValue, currentLine.Substring( _
                          charIndex + 1))
                    End If
                End If
            Loop Until stream.EndOfStream
        End Using
    End Sub
 
    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) _
      Handles Button2.Click
        Dim codeValue As Integer
 
        If Integer.TryParse(TextBox1.Text, codeValue) Then
            If codeMessages.ContainsKey(codeValue) Then
                MessageBox.Show(codeMessages(codeValue))
            End If
        Else
            MessageBox.Show("Code unbekannt")
        End If
    End Sub
 
End Class