private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            char c = e.KeyChar;
            if (char.IsLetter(c))
                label1.Text = "字母";
            else if (char.IsDigit(c))
                label1.Text = "数字";
            else if (char.IsPunctuation(c))
                label1.Text = "标点";
            else
                label1.Text = "其他";
        }