private void button_click(object sender, EventArgs e)
        {
            if ((TResult.Text == "0") || (operationPerformed))
            {
                TResult.Clear();
                dotCount = 0;
            }

            operationPerformed = false;
            Button b = (Button)sender;

            if (b.Text == "." && dotCount < 1)
            {
                dotCount++;
                TResult.Text = TResult.Text + b.Text;
            }
            if (b.Text != ".")
            {
                TResult.Text = TResult.Text + b.Text;
            }
        }