求C#大神，求指导。。急。。！！！
private void button1_Click(object sender, EventArgs e)
        {
           
            if (textBox4.Text == "")
            {
                MessageBox.Show("请输入年龄！");
                return;
            }
            if (textBox7.Text == "")
            {
                MessageBox.Show("请输入工龄！");
                return;
            }
            if (comboBox1.Text == "")
            {
                MessageBox.Show("请选择部门！");
                return;
            }
            int age = Convert.ToInt32(textBox4.Text);
            int gonglin = Convert.ToInt32(textBox7.Text);

            String cnno = "Data Source=HP-PC;Initial Catalog=FIRST;Integrated Security=True;Pooling=False";
            SqlConnection connection = new SqlConnection(cnno);
            string sql = string.Format("Insert into Xinxi values('{0}','{1}','{2}',{3},'{4}','{5}',{6},'{7}','{8}','{9}') ", textBox1.Text, textBox2.Text, textBox3.Text, age, comboBox1.Text, textBox6.Text, gonglin, textBox8.Text, textBox9.Text, textBox10.Text);
           
            connection.Open();
            SqlCommand command = new SqlCommand(sql, connection);
            //int num = Convert.ToInt32(command.ExecuteScalar());
            int num = command.ExecuteNonQuery();
            try
            {
                if (num > 0)
                {

                    MessageBox.Show("添加成功！");
&