private void RidgeLengthTextBox_GotFocus(object sender, RoutedEventArgs e)
 {
     if (RidgeLengthTextBox.Text == string.Empty)
     {
         RidgeLengthTextBox.Text = "0";
     }
     RidgeLengthTextBox.SelectAll(); b = false;
 }
        private void RidgeLengthTextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            int c = 0;


            if (!int.TryParse(RidgeLengthTextBox.Text, out c))
            {
                MessageBox.Show("Enter length to nearest inch", "Invalid Entry");
            }
            if (RidgeLengthTextBox.Text == string.Empty)
            {
                RidgeLengthTextBox.Text = "0"; RidgeLengthTextBox.SelectAll();
            }
            if (b == false)
            {
                SqFtTotal.Text = FigureSqFt(int.Parse(EaveLengthTextBox.Text), int.Parse(RakeLengthTextBox.Text), int.Parse(RidgeLengthTextBox.Text)).ToString();
            }
        }