数据库问题,在线等

 private void button1_Click_1(object sender, EventArgs e)
        {
            MessageBox.Show("请确认信息是否误");
            SqlConnection sqlconn = new SqlConnection(@"server=(local);database=xmgl;uid=sa;pwd=;Connection Timeout=30");
            sqlconn.Open();            string a = "insert into money values('" + textBox3.Text + "','" + textBox2.Text + "'," + Convert.ToDecimal(textBox1.Text) + ",'" + comboBox1.Text + "',null," +dateTimePicker1.Value + "," + dateTimePicker2.Value+ "," +dateTimePicker3.Value + "," +dateTimePicker4.Value+ ")";
            SqlCommand sqlcomm = new SqlCommand(a, sqlconn);            sqlcomm.ExecuteNonQuery();
            sqlconn.Close();
            this.Close();
        }
提示我字符格式有问题