c#2_14.cs

private void StartButton_Click(object sender, EventArgs e)
{
gameActive = true;
     for (var x = 0; x < 3; x++)
     {
         for (var y = 0; y < 3; y++)
         {
             fields[x][y] = Player.None;
         }
     }
     Button0_0.Content = "";
     Button0_1.Content = "";
     Button0_2.Content = "";

     Button1_0.Content = "";
     Button1_1.Content = "";
     Button1_2.Content = "";

     Button2_0.Content = "";
     Button2_1.Content = "";
     Button2_2.Content = "";

     fieldsMarked = 0;
}