Public Class Form1

    Private Sub btnLiteral_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLiteral.Click
        Dim a As Integer
        a = 4
        lstBox.Items.Add(a)
    End Sub

    Private Sub txtNumber_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtNumber.TextChanged
        Dim b As Integer
        b = CInt(txtNumber.Text)
        lstBox.Items.Add(b)
    End Sub

    Private Sub btnInputBox_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnInputBox.Click
        Dim c As Integer
        c = CInt(InputBox("Enter an interger", "Intger"))
        lstBox.Items.Add(c)
    End Sub
End Class