Form1.vb

Public Class Form1
    Dim gCurrentMove As Integer = 0

    Private Sub Button1A_Click(sender As Object, e As EventArgs) Handles Button1A.Click
        ' Check to see if the button's text is empty.
        ' If it's not empty, let's not waste our time
        If Button1A.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            ' Set button text to O
            Button1A.Text = "O"
            ' Set gCurrentMove to 1
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            ' Set button text to X
            Button1A.Text = "X"
            ' Set gCurrentMove to 0
            gCurrentMove = 0
        End If
    End Sub

    Private Sub Button1B_Click(sender As Object, e As EventArgs) Handles Button1B.Click
        If Button1B.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button1B.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button1B.Text = "X"
            gCurrentMove = 0
        End If
    End Sub


    Private Sub Button1C_Click(sender As Object, e As EventArgs) Handles Button1C.Click
        If Button1C.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button1C.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button1C.Text = "X"
            gCurrentMove = 0
        End If
    End Sub

    Private Sub Button2A_Click(sender As Object, e As EventArgs) Handles Button2A.Click
        If Button2A.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button2A.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button2A.Text = "X"
            gCurrentMove = 0
        End If
    End Sub


    Private Sub Button2B_Click(sender As Object, e As EventArgs) Handles Button2B.Click
        If Button2B.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button2B.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button2B.Text = "X"
            gCurrentMove = 0
        End If
    End Sub

    Private Sub Button2C_Click(sender As Object, e As EventArgs) Handles Button2C.Click
        If Button2C.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button2C.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button2C.Text = "X"
            gCurrentMove = 0
        End If
    End Sub


    Private Sub Button3A_Click(sender As Object, e As EventArgs) Handles Button3A.Click
        If Button3A.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button3A.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button3A.Text = "X"
            gCurrentMove = 0
        End If
    End Sub


    Private Sub Button3B_Click(sender As Object, e As EventArgs) Handles Button3B.Click
        If Button3B.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button3B.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button3B.Text = "X"
            gCurrentMove = 0
        End If
    End Sub

    Private Sub Button3C_Click(sender As Object, e As EventArgs) Handles Button3C.Click
        If Button3C.Text <> "" Then
            Return
        End If

        If gCurrentMove = 0 Then
            Button3C.Text = "O"
            gCurrentMove = 1
        ElseIf gCurrentMove = 1 Then
            Button3C.Text = "X"
            gCurrentMove = 0
        End If
    End Sub
End Class