Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged If TextBox1.Text.Length > 0 Then Dim i As Integer Try i = Convert.ToInt32(TextBox1.Text) Catch ex As System.FormatException TextBox1.Text = "" MessageBox.Show("Veuillez entrer un chiffre!", "Chiffre", MessageBoxButtons.OK, MessageBoxIcon.Exclamation) End Try End If End Sub