คำสั่ง font size

Public Class Form1
    Dim num As Integer
    Private Sub cmbNum_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbNum.SelectedIndexChanged
        txtShow.Text = cmbNum.Text
        num = cmbNum.Text
        txtShow.Font = New Font(txtShow.Font.FontFamily, num, txtShow.Font.Style)
    End Sub

    Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        num = txtShow.Text
        txtShow.Font = New Font(txtShow.Font.FontFamily, num + 1, txtShow.Font.Style)
        txtShow.Text = num + 1
    End Sub

    Private Sub btnDelete_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnDelete.Click
        num = txtShow.Text
        txtShow.Font = New Font(txtShow.Font.FontFamily, num - 1, txtShow.Font.Style)
        txtShow.Text = num - 1
    End Sub
End Class